To provide a buckle which is designed to prevent a belt from slackening by solidly securing the belt distributed to an adjusting section in a male body, when a housing in a female body and an inserting member in the male body are engaged with each other.

A supporting strut 18 is mounted on an upper portion of sidewalls 6 at an inserting gate 5 of the flat housing 4 in the female body, the supporting strut is disposed in a middle part with a crooked portion 19 projecting outward in U shape, a tongue-like pushing piece 20 projecting outward is formed in one piece with the crooked portion 19, the pushing piece 20 pressurizes a belt hanging strut 40 at the adjusting section 44 in the male body 2 when the inserting member, an inserting leg portion 45 in the male body 2, is inserted from the inserting gate 5 and is engaged, the belt hung around the belt hanging strut 40 is pinchingly held and secured, and belt slackness prevention is realized.