A clutch mechanism in which a pressure receiving member is attached to two side frames of a seat back of a vehicle seat so as to be rotatable about rotation axes extending in a widthwise direction and in which when the pressure receiving member is rotated by a pressing load of an passenger sitting on the vehicle seat, the pressing load is selectively transmitted to an operation bracket pivotally connected to the rotation axes such that the operation bracket is rotated in the same direction as the pressure receiving member. When the pressure receiving member receives a quick pressing load, the operation bracket rotates while being mechanically integrated with the pressure receiving member, so that the pressing load can be transmitted to the operation bracket. When the pressure receiving member receives a slow pressing load, the operation bracket does not rotate, and only the pressure receiving member rotates, so that the transmission of the pressing load can be blocked.