An edge of a guide hole includes a first contact portion, a second contact portion, and a guide portion. The first contact portion is in contact with the second connecting pin while the second connecting pin is positioned in the lock actuation position. The second contact portion is in contact with the second connecting pin while the second connecting pin is positioned in the lock release position. The guide portion extends in a direction intersecting the movement direction of the second connecting pin between the first contact portion and the second contact portion. The guide portion is pressed by the second connecting pin that moves from the lock actuation position to the lock release position in order to resist the urging force of an urging member and cause the second lock member to move from the locked position to the unlocked position.