To provide a novel buckle for a belt such as a knapsack belt of a rucksack and a shoulder belt for a bag or case, which has such convenience that a consumer (or a workman of a maker) can arbitrarily attach it at any time after attaching the belt to the main body of the rucksack or the like.

The buckle which comprises a frame body 1 and a medium pestle 2 differing from this and in which a fixing portion for a user to arbitrarily fix the medium pestle to the frame body 1 is placed in the middle part of both right and left sides 3 and 4 and both edges of the medium pestle 2.