A side release buckle includes a plug and a socket into which the plug is inserted for engagement. The plug includes: a base provided with a belt attachment; a pair of legs projecting from the base; an engaging portion formed to the legs; and a connecting portion connecting the legs to each other. The socket includes: a body provided with a belt attachment and an insertion opening; a housing space formed in the body and housing the legs inserted from the insertion opening; an engaged portion formed in the body and engageable with the engaging portion; and a cutout dented toward the insertion opening from an edge of the belt attachment. The cutout is formed over an area surrounded by the legs and the connecting portion when the legs and the connecting portion are housed in the housing space while the engaging portion and the engaged portion are engaged.