Abstract: A four wheel driving power transmission is provided which is interposed between an input shaft and an output shaft in a driving power transmitting system for the wheels of a four wheel drive car. The transmission is provided with a member in association with one of the input shaft and the output shaft and a cylindrical casing in association with the other. The casing seals therein a working fluid in a fluid-tight manner and houses a fluid pressure pump operating by relative rotation of the casing with respect to the shaft, a piston actuated by discharge pressure of the pump, and a sliding clutch for engaging the shaft with the cylindrical casing through operation of the piston.