Inclusion Criteria:  Preliminary study - Establishment of Ga-68 PSMA-11 PET/CT imaging conditions (three subjects)  Equal or more than 19 years old Biopsy proven prostate cancer patients with high risk group (serum PSA> 20 ng/ml) or metastatic prostate cancer patients identified on other imaging modalities prior to Ga-68 PSMA-11 PET/CT imaging  Main study (40 subjects)  Equal or more than 19 years old Patients who had previously undergone radical prostatectomy and were histologically diagnosed with prostate cancer. Patients identified with biochemical recurrence through serum PSA tests during postoperative follow-up (Serum PSA level equal or more than 0.2 ng/ml at least two times and one of the tests was conducted within one month before consent to the study) in which metastatic lesions were not found or uncertain in standard imaging modalities (abdominal/Pelvic CT, bone scan). Patients who can be followed up clinically, including serum PSA tests, for at least 6 months after consent to the study at this hospital.  Exclusion Criteria:  Preliminary study - Establishment of Ga-68 PSMA-11 PET/CT imaging conditions (three subjects)  Primary cancer other than prostate cancer has been previously diagnosed or has occurred simultaneously with prostate cancer; Previous primary cancer other than prostate cancer is a local disease and has been cured completely shall be an exception. Subjects who has concurrent severe and/or uncontrolled and/or unstable medical disease (e.g. congestive heart failure, acute myocardial infarction, severe pulmonary disease, chronic renal or hepatic disease which could compromise participation in the study) based on the judgment of the investigator Subjects who cannot perform PET/CT imaging due to claustrophobia, dyskinesia, anxiety disorders, etc.  Main study (40 subjects)  Primary cancer other than prostate cancer has been previously diagnosed or has occurred simultaneously with prostate cancer; Previous primary cancer other than prostate cancer is a local disease and has been cured completely shall be an exception. Subjects who cannot perform CT, bone scan, etc., which are standard diagnostic procedures for lesion localization in case of biochemical recurrence. Subjects who has concurrent severe and/or uncontrolled and/or unstable medical disease (e.g. congestive heart failure, acute myocardial infarction, severe pulmonary disease, chronic renal or hepatic disease which could compromise participation in the study) based on the judgment of the investigator Subjects who cannot perform PET/CT imaging due to claustrophobia, dyskinesia, anxiety disorders, etc. Subjects who might make the collection of complete data difficult or impossible due to personal circumstances or other reasons, in the judgment of the investigator.