There is provided a booster of a braking force 1 which drives a master cylinder by boosting an operation force of a brake pedal 100 in accordance with a movement amount of an input member 4 that reciprocates by an operation of the brake pedal 100, including: the input member 4 of which one end is linked to the brake pedal 100, which is inserted and fitted to the inside of a control housing 3 installed in a housing 2, and which is provided to be freely relatively slidable in an axial direction; and damping members 22, 31, and 32 which are provided at a part at which the input member 4 and the housing 2 abut against each other, or at a position which can be linked or abut against a part of the input member 4, in which, when the input member 4 moves to return when releasing an operation of the brake pedal 100, when the input member 4 abuts against the housing 2, the damping members 22, 31, and 32 perform an impact absorbing and damping action.