A buffer which can achieve a buffering effect corresponding to the speed of a sliding door is provided. Corresponding to the abutment force of an engagement pin 3 which is on a sliding door 2 with respect to a retaining recessed portion 67 of a hook body 61 which is slidably provided in a case body, an engagement stepped portion 71 of the hook body 61 presses a pressing member 44, and a brake pad 47 of the pressing member 44 and a brake pad 39 of a slider 31 come into sliding contact with a brake plate 28.