A buckle device consisting a tongue plate to be connected to a webbing, and a buckle body into and from which the tongue plate is inserted and extracted, wherein said buckle body comprises: - a frame; - a hook member pivotably mounted on the frame, said hook member being adapted to pivot to come into engagement with the tongue plate upon insertion of the tongue plate and being pivotally urged in the disengaging direction all the time; - a release button made of plastics and for releasing the engagement between the hook member and the tongue plate; and - a lock bar movable to a first position, in which the lock bar inhibits pivoting of the hook member in the disengaging direction, by an urging force of a biasing member when said hook member is being engaged with the tongue plate, and said lock bar also movable to a second position, in which the lock bar allows pivoting of the hook member in the disengagement direction, by being pushed by the release button upon disengaging operation of the release button, said buckle device being characterized in that - the frame comprises: a base plate part; a pair of opposing side plate parts rising from both left and right side edges of the base plate part; a pair of long holes formed in the side plate parts; a pair of stopper parts for stopping the release button against the urging force of the biasing member urging the lock bar, said stopper parts being integrally formed with the frame on the side plate parts of frame; - the lock bar is passed through the pair of long holes and mounted across the pair of side plate parts with both end parts of the lock bar projecting outwardly from the pair of side plate parts; and - a stop restriction part, which receives the lock bar against the urging force of the biasing member when the lock bar is moved from the second position to the first position by the urging force, is integrally formed with the release button, the stop restriction part being comprised of a pair of receiving parts for receiving the both end parts of the lock bar which project outwardly from the pair of side plate parts. - a frame; - a hook member pivotably mounted on the frame, said hook member being adapted to pivot to come into engagement with the tongue plate upon insertion of the tongue plate and being pivotally urged in the disengaging direction all the time; - a release button made of plastics and for releasing the engagement between the hook member and the tongue plate; and - a lock bar movable to a first position, in which the lock bar inhibits pivoting of the hook member in the disengaging direction, by an urging force of a biasing member when said hook member is being engaged with the tongue plate, and said lock bar also movable to a second position, in which the lock bar allows pivoting of the hook member in the disengagement direction, by being pushed by the release button upon disengaging operation of the release button, - the frame comprises: a base plate part; a pair of opposing side plate parts rising from both left and right side edges of the base plate part; a pair of long holes formed in the side plate parts; a pair of stopper parts for stopping the release button against the urging force of the biasing member urging the lock bar, said stopper parts being integrally formed with the frame on the side plate parts of frame; - the lock bar is passed through the pair of long holes and mounted across the pair of side plate parts with both end parts of the lock bar projecting outwardly from the pair of side plate parts; and - a stop restriction part, which receives the lock bar against the urging force of the biasing member when the lock bar is moved from the second position to the first position by the urging force, is integrally formed with the release button, the stop restriction part being comprised of a pair of receiving parts for receiving the both end parts of the lock bar which project outwardly from the pair of side plate parts. a base plate part; a pair of opposing side plate parts rising from both left and right side edges of the base plate part; a pair of long holes formed in the side plate parts; a pair of stopper parts for stopping the release button against the urging force of the biasing member urging the lock bar, said stopper parts being integrally formed with the frame on the side plate parts of frame; - the lock bar is passed through the pair of long holes and mounted across the pair of side plate parts with both end parts of the lock bar projecting outwardly from the pair of side plate parts; and - a stop restriction part, which receives the lock bar against the urging force of the biasing member when the lock bar is moved from the second position to the first position by the urging force, is integrally formed with the release button, the stop restriction part being comprised of a pair of receiving parts for receiving the both end parts of the lock bar which project outwardly from the pair of side plate parts.