In this article, psychiatric arguments regarding criminal responsibility in schizophrenia are reviewed, and it is pointed out that the arguments have been influenced by the theory of process psychosis. Moreover, two cases judged on the basis of the activation-recurrence phenomenon are exemplified, and fundamental issues are discussed. Investigating the mental state just before the crime helps when deliberating over criminal responsibility. A study of the activation-recurrence phenomenon,conducted by Shinkai and Miyasaka, contributes toward clarifying the recurrence of the micropsychotic state during the criminal act. Generally, schizophrenia is characterized by an alternation between the micropsychotic and basic normal states, and classified clinically into severe, moderate, and mild according to the level of susceptibility to the occurrence of the activation-recurrence phenomenon. Differentiating between the form and contents of the micropsychotic state is of marked importance in schizophrenia. In addition,identifying the form facilitates the distinction between behaviors while sane and those during schizophrenic episodes. Practically, the activating stimuli, which are likely to trigger the micropsychotic state, are applied in the interview to establish the psychiatric testimony based upon the activation-recurrence phenomenon. After the diagnosis of schizophrenia has been confirmed, the examinee is exposed to the stimuli possibly activating the micropsychotic state during the criminal act. Observing the recurrence of the micropsychotic state and its frequency enables estimation of the susceptibility to the occurrence of the activation-recurrence phenomenon and the mental state during the criminal act. Therefore,if a micropsychotic state during the criminal act can be confirmed, the inability to be held legally responsible is postulated. In contrast,if a micropsychotic state during the criminal act cannot be confirmed,the specialist giving the psychiatric testimony should conclude that the crime was most likely undertaken while sane, taking into account the objective circumstantial evidence and the suspect's coherent actions during the crime. Furthermore,in this article,the concept Trugerinnerung,which is a subjective abnormal experience confusing the present and past（a disorganization of memory）is revaluated,and the possibility of concluding that the criminal act was performed with a normal psychology is discussed.