PURPOSE: To improve starting ability and improve durability by providing an orifice having a specified condition to a secondary pressure inflowing circuit of a pilot pressure hydraulic chamber of a secondary control valve, and a check valve on the solenoid side of the pilot pressure hydraulic chamber.

CONSTITUTION: When solenoid current Is becomes nearly zero due to cutoff of solenoid wiring and drop in power supply at the time of starting of engine, an armature 55 is advanced by a spring 56 in a secondary pressure control valve 50 under secondary pressure control so as for a valve disc 58 to fully close a drain port 51e of a pilot hydraulic chamber 51b. At this time, the arma ture 55 opens a check valve 59, and drains a specific quantity of oil through the check valve 59 to the oil entering the pilot hydraulic chamber 51b through an orifice 52f of a passage 52e. Thus, pilot pressure Pc of the pilot hydraulic chamber 51b is controlled to a specified hydraulic pressure smaller than a maxi mum pressure, and thereby secondary pressure Ps becomes an intermediate, specified hydraulic pressure Po.