Patent ID: 7278508

Claim:
A control system of an industrial truck, comprising: a first switch for an industrial truck body, said first switch being operable to detect whether or not an operator sits down on a seat and to carry out a first operation based upon a detection result by said first switch; a second switch for the industrial truck body, said second switch being operable to detect whether or not a device for operating an actuator is being operated and to carry out a second operation based upon a detection result by said second switch; and a hydraulic circuit which is usable for operating the actuator, said hydraulic circuit containing hydraulic fluid, and said hydraulic circuit including: a control valve including a spool whose position is changeable by the device for operating the actuator, a first circulating line that includes said control valve, the hydraulic fluid being able to circulate through said first circulating line, a hydraulic line usable to connect said spool with the actuator, the hydraulic fluid being able to pass through the hydraulic line, a drive lock valve provided for said hydraulic line, a second circulating line connected in parallel with said first circulating line, said second circulating line not including said control valve, wherein the hydraulic fluid can bypass said control valve through said second circulating line, and an unloading valve operable in response to said first operation and included in said second circulating line, wherein said drive lock valve is operable to block said hydraulic line based on one of said first operation and said first and second operations, and wherein said unloading valve is operable to open to connect a point upstream of said unloading valve directly with a hydraulic fluid tank based on one of said first operation and said first and second operations.