• •CAPS-SX score (at week 12)
  

• •Cerebral regional blood flow •CGI-GI •CGI-SI •CAPS-SX score (at week 4 and 8), subtotal in re-experiencing, avoidance and numbing, and increased arousal symptom •Study continuation rate [ Time Frame: A total of 18-21 Weeks ]
  
• Change from the baseline of regional blood flow; Proportion of responders of CGI Global Improvement; Change from the baseline of CGI Severity of Illness
  
• Change from the baseline of CAPS-SX total score (at week4 and week 8); Change from the baseline of CAPS-SX score relating re-experiencing; Change from the baseline of CAPS-SX score relating avoidance and numbing
  
• Change from the baseline of CAPS-SX score relating increased arousal symptom; Study continuation rate
  

Inclusion Criteria:

• Patients who are primarily diagnosed with PTSD (Posttraumatic Stress Disorder: 309.81) using DSM-IV-TR criteria. The CAPS-DX (Clinician-Administered PTSD Scale-DX) and M.I.N.I. (The Mini International Neuropsychiatric Interview, Japanese version 5.0.0. [2003]) will be used for diagnosis
• Pathologic condition: Patients who experienced a motor vehicle accident (MVA) with severe or potential severe physical injury more than 3 months ago but less than 12 months ago
• Patients aged 20 and <65 at the time of signing the Informed consent
• Male and female patients
• Inpatient/outpatient status: Both are permitted
• Patients who are able to give written informed consent in person (i.e., patients who are capable of giving written informed consent on their own)
• Patients whose combined score of the CAPS-SX standard B, C, and D is over 50

Exclusion Criteria:

• Patients primarily diagnosed with a DSM-IV-TR Axis I disorder other than PTSD (e.g. major depressive disorder, dysthymic disorder, specific phobia [simple phobia], obsessive-compulsive disorder, panic disorder, etc.) within 6 months of week -4 (start of baseline phase)
• Patients presenting with a current major depressive episode that preceded the diagnosis of PTSD
• Patients receiving disability payments due to PTSD or other psychiatric diseases
• Patients currently engaged in compensation litigation whereby personal gain would be achieved from prolonged symptoms of PTSD or any other psychiatric disorders
• Patients who meet the DSM-IV-TR criteria for substance abuse or dependence (alcohol or drugs) within 6 months of Week -4 (start of baseline phase)
• Patients with history of a suicide attempt within 6 months before Week -4 (start of baseline phase), or have, in the opinion of the investigator, "C. high risk of suicide" according to the MINI at Week -4
• Patients who are pregnant, lactating or of childbearing potential and are likely to become pregnant
• Patients receiving electro-convulsive therapy (ECT) prior to Week -4 (start of baseline phase)
• Patients receiving another investigational product within 12 weeks before Week -4 (start of baseline phase)
• Patients with a history or complication of manic psychosis
• Patients with a history or complication of convulsive disorder (epilepsy, etc.)
• Patients with a diagnosis or complication of a cognitive disorder (MMSE ?24 points)
• Patients with a history and complication of serious cerebral organic disorder. (e.g. cerebrovascular disorder, meningitis, degenerative disease and other neurological disorders and seizures; however, bleeding in the upper arachnoid membrane should not be excluded)
• Patients unable or unwilling to undergo the fMRI procedure (e.g., cerebrovascular clipping surgery, pacemaker, any internal metals with magnetism, and claustrophobia)
• Patients with glaucoma
• Patients with a known tendency for bleeding or those with predisposing conditions
• Patients with a history of hypersensitivity to paroxetine
• Patients with serious physical symptoms (cardiac, hepatic and renal dysfunction, or hematopoietic dysfunction, etc.). For seriousness, Grade 3 of "Criteria for seriousness of adverse reactions to drugs, etc. (Yakuan No.80)" is used as an index
• Patients with a history or complication of cancer or malignant tumour
• Patients with chronic hepatitis type B and/or C which is positive of hepatitis B surface antigen (HBsAg) and/or hepatitis C antibody
• Others whom the investigator or sub-investigator considers ineligible for or unable to participate in the investigation
• Criteria at Week 0 (start of Treatment Phase):

Subjects whose drug compliance rate for Drug 1 (Run-in Phase placebo) is <80% between Week -4 and Week 0;

Subjects whose CAPS-SX total score of the standard B, C, and D at Week 0 varied by 25% or more compared with those at Week -2