To provide a work chucking device which is small in number of parts, free from any danger of a worker's hand being caught thereby, and high in safety.

In a hydraulic cylinder 14 to operate a chucking lever 25 to hold a work, the piston bearing area of a head side chamber 20 is set to be larger than the piston bearing area of a rod side chamber 21 to be demarcated by a piston 18, the chucking lever is chucked by introducing the pressurized fluid into the head side chamber 20 from a control valve 35 to switch the direction to feed the pressurized fluid between the head side chamber 20 and the rod side chamber 21, the chucking lever is unchucked by introducing the pressurized fluid into the rod side chamber 21, and a communication switching valve 41 to switch the regular position at which the rod side chamber 21 of the hydraulic cylinder 14 is connected to the control valve 35 and the communication position at which the rod side chamber 21 communicating with the head side chamber 20, is provided.