A buckle that is compact in a longitudinal direction and uses an unlatching force that may be effectively applied to a latch member when releasing a tongue from a buckle. The buckle is configured so that as an operation button is manipulated in the unlatching direction from a state in which a tongue and a latching portion of a latch member are latched, the slider moves so that the inclined face of a pressed portion of the slider comes in contact with the inclined face of a pressing portion of an ejector and presses the ejector. Then, the ejector is spaced from the tongue and the biasing force of an ejector spring is effectively applied to the latch member via the ejector and the slider in the unlatching direction. An unlatching force is thereby applied to the latch member so that the latch member pivots in the unlatching direction, causing release of the tongue.