JACK DEVICE AND WORK MACHINE EQUIPPED WITH SAME

Provided is a jack device (20) rendering an operation of changing the posture of a jack cylinder (41) easy without using a device that actively changes the posture. The jack device (20) includes an arm (30), a jack body (40) including the jack cylinder (41), and a reaction-force application unit (60) supported by the arm (30). The reaction-force application unit (60) makes a reaction-force moment act on the jack body (40) in all postures from the upright posture to the storage posture in response to a force applied from the jack body (40). The reaction-force application unit (60) makes a reaction-force moment (Mr) greater than a self-weight moment (Ms) act on the jack body (40) in the storage posture and makes a reaction-force moment (Mr) smaller than the self-weight moment (Ms) act on the jack body (40) in the upright posture.