Plug and Buckle

A plug and a socket constitute a buckle. The plug includes a plug base and a pair of legs. At least one of the pair of legs includes a first extension extending from the plug base in an insertion direction of the plug, a second extension extending from the first extension in an inward width direction of the plug, an engagement portion provided on the first extension or the second extension to be engageable with a to-be-engaged portion of the socket in a detachment direction of the plug, and an operation portion provided on the second extension. When a force in the detachment direction is applied on the operation portion, the first extension is elastically deformed in the width direction of the plug in such a manner that a position of the engagement portion shifts from an engagement position to a disengagement position with respect to the to-be-engaged portion.