LOCK MECHANISM

A lock mechanism includes a lock shaft (12) attached to a first bracket (3), a lock shaft support shaft (11), and a biasing spring that biases the lock shaft (12) in a direction in which the lock shaft (12) abuts against a second bracket (4). Rotational movement prevention stoppers (17 and 18) abut against each other, thereby preventing rotation of the first bracket (3) and the second bracket (4) in the locking direction and a backlash therebetween. The lock shaft (12) comes into contact with both a first side face (21) and a second side face (22), and a pair of tangents (25 and 26) to the lock shaft (12) are set to form a wedge (27), so that rotation of the first bracket (3) and the second bracket (4) in the locking direction and the opposite direction is prevented without backlash.