In Japan,forensic psychiatrists are generally reluctant to detect malingering. This trend may have led to the present state whereby studies on malingering are very scarce. The fundamental problem here is that we have no concept that malingering must be proved and no methodology to actually prove it.
 The author has presented procedures which prove that a defendant who has been regarded as showing prison psychosis is malingering. First of all, it is important to specify certain feigned symptoms as much as possible by making full use of exploratory questions which include using techniques involving changing the condition of dialogue. It is also decisive to reinforce the former（observational data based on exploration）by examining collateral information carefully.
 This procedure has made it possible to verify that most psychotic symptoms are a feigned psychopathology. It is certain that an external incentive（evading criminal prosecution）exists. Moreover, there is no mental disease which could produce such psychotic symptoms. As these factors are acknowledged,it enables us to conclude whether a defendant shows malingering.
 On the other hand, pseudologia phantastica has been regarded as exclusively characterogenic. However the possibility that it could be a reaction to circumstances has been pointed out but has regrettably gone unnoticed. Plausible statements about the early personal histories of defendants and most psychotic symptoms after detention are fabricated stories which are phantastic and, moreover, defensive concerning the external incentive mentioned above. Therefore,from another point of view,it could be said that narratives of defendants can be classified as a reactive type of pseudologia phantastica.