A locking device includes a lock portion on one of a fixed body or an opening/closing body, a rod on the other member, and a protrusion protruding from the other member. The rod has a recess surrounded by a pair of first walls facing each other in a sliding direction of the rod and a pair of second walls facing each other in a direction orthogonal to the sliding direction. A first elastic piece extends from one of the first walls toward the other and applies an elastic force against a tip end surface of the protrusion, and a pair of second elastic pieces extend from the second walls. Each of the second elastic pieces has a receiving surface that engages with a back surface of a flange portion of the protrusion, and is configured to elastically abut against a side surface of the protrusion.