To reduce the inertial rotation of a motor at running down a slope and enhance the durability by holding a two-speed running motor on the low- speed side for a fixed period of time after the vehicle body has started running.

Using a speed setting switch 23, the capacity of a running motor 14 is set to the high speed side or low speed side through a controller 24, speed selector valve 17, etc. A direction control valve 18 is changed over to be operated by an operating lever and an operating mechanism 20 through a pilot pipeline 19. Using a pressure sensor 26, the controller 24 senses a change in the pilot pressure as the start of vehicle running, and holds the capacity of the motor 14 to the low speed side until a fixed period of time has elapsed since the running started irrespective of the setting position of the switch 23.