A changing device easily and safely changes the posture of the backstop of a crane between a support posture and a storage posture. The backstop posture changing device is provided with a first support member, a second support member, a push-up mechanism, and a connection member. The first support member and the second support member are rotationally connected to a backstop and a lower boom respectively. When a cylinder rod of the push-up mechanism is extended with respect to a cylinder body, a push-up member pushes up the first support member and the posture of the backstop is changed from a storage posture on the lower boom to a support posture in which it is possible to support a boom while the crane is in a working posture.