<p>Disclosed is side release buckle including a plug (10) and a socket (20) into which the plug is inserted and engaged. The plug (10) has a base portion (11) that includes a belt fitting portion (19) and a pair of leg portions (12), and engaging portions (14) formed in each of the leg portions (12). The socket (20) has a main body (21) that includes a belt fitting portion (29) and an insert hole (22), a housing space (23) formed in the main body (21) and able to house the leg portions (12) inserted through the insert hole (22), and engaged portions (24) formed in the main body (21) with which the engaging portions (14) are able to engage. The main body (21) includes an undulation (26) provided continuously in the top side or bottom side thereof in at least the direction of insertion of either of the leg portions (12).</p>
