A control system of an industrial truck includes a first switch, a second
switch and a hydraulic circuit. The first switch detects whether an
operator sits on a seat, and carries out a first operation based on the
result. The second switch detects whether a device for operating an
actuator is operated, and carries out a second operation based on the
result. The hydraulic circuit is used for operating the actuator. It a
control valve, a first circulating line, a hydraulic line and a drive
lock valve. The control valve includes a spool whose position is changed
by the device. The first circulating line includes the control valve,
through which the hydraulic fluid circulates. The hydraulic line connects
the spool with the actuator. The drive lock valve is provided for the
hydraulic line and blocks the hydraulic line, based on the first
operation and/or the second operation.