A buckle apparatus for safety belt assembly, comprises a tongue member provided on opposed side edges with notches, a base plate member having a portion where said tongue member is inserted and being formed on the opposed sides thereof with guide grooves substantially perpendicular to the direction of the tongue insertion, a tongue latching means including a pair of tongue latching members, the tongue latching members being slidable along the respective guide grooves of the base plate member in a direction to substantially perpendicular to the direction of the tongue insertion, means for biasing said tongue latching members so that the tongue latching members may engage the respective notches of the tongue member, when the tongue member is inserted into the base plate member, to latch the tongue member, and operable means including cam portions for moving said tongue latching members against the force of said biasing means to unlatch the tongue member.