JACK DEVICE AND WORK MACHINE EQUIPPED WITH SAME

Provided is a jack device rendering an operation of changing the posture of a jack cylinder easy without using a device that actively changes the posture. The jack device includes an arm, a jack body including the jack cylinder, and a reaction-force application unit supported by the arm. The reaction-force application unit makes a reaction-force moment act on the jack body in all postures from the upright posture to the storage posture in response to a force applied from the jack body. The reaction-force application unit makes a reaction-force moment greater than a self-weight moment act on the jack body in the storage posture and makes a reaction-force moment smaller than the self-weight moment act on the jack body in the upright posture.