To easily create a double-locked state in a buckle having a double-locking function.

The buckle is composed of a buckle female member and a buckle male member. An insertion part 6 of the buckle male member includes a resilient engaging piece 6a which springs when inserted into the buckle female member F to a first position to be engaged with an engaged part 1n of the buckle female member F. The buckle female member F includes a locking member 2 for preventing resilient deformation of the resilient engaging piece 6a of the buckle male member M in the direction of releasing the engagement at a locking position. The locking member is movable between the locking position and an unlocking position. The buckle female member F also has a holding means 1b for holding the locking member 2 at the unlocking position against urging by an urging means 3 for urging the locking member 2 toward the locking position. The hold of the locking member 2 by the holding means 1b is released when the insertion part 6 of the buckle male member M at the first position is inserted into the buckle female member F further to a second position deeper than the first position.