This is a review on the longitudinal transformation of the Japanese trousers, which is prepared as a pre-study for the comparative analysis of the forms of Korean and Japanese folk trousers. The special traits of the Japanese trousers are found to be as follows: 1) The Japanese trousers seem to have their root in the Northern-Asian or Schithian culture. 2) While the ancient forms of Japanese trousers, esp., those of the 8C before include the same types as Korean folk trousers, the Medieval and Recent era trousers quite differ and transform themselves into the unique Japanese type. 3) All Japanese trousers can largely be classified into formal and functional trousers. Formal trousers play important role as one of the ceremonial wardrobe and are treated rather as an outermost-wear than as an inner-wear. 4) The formal trousers have skirt-like features with much fullness as are presented in many deep pleats, long crotch lines and long sashes connected to the belt; the femine trousers even omit crotch line. 5) The principal forms of Japanese trousers consist of I, $wedge,;wedge$; the $lambda$ form of Korean and Chinese type had never existed. 6) Varieties of the composite type of Japanese-Western style appear among the trousers of recent time.