To obtain a buffer capable of being reduced in weight and the number of components and being inexpensive.

A buffer includes: a pair of guide parts 5 and 7 which have locking guide holes 27 and 29 for a stopper provided at juxtaposition-direction outer ends of linear guide holes 23 and 25 juxtaposed along a movement direction of a sliding door 65 on a base 3; a pair of movable block bodies 9 and 11 which are movably supported along the linear guide holes 23 and 25 of the guide parts 5 and 7, respectively, and which are engaged and held by guidance in the locking guide holes 27 and 29; an engaging recess 13 or an engaging recess 15, which is formed in the movable block body 9 or the movable block body 11, opened in a direction crossing the linear guide holes 23 and 25, and engaged with a protrusion 61a or a protrusion 61b in an opening 63; a single spring 17 which is interposed between the pair of movable block bodies 9 and 11 and which urges both the movable block bodies 9 and 11 in such a manner as to attract them along the linear guide holes 23 and 25; and a single linear damper 19 which is interposed between the pair of movable block bodies 9 and 11 and which damps an urging force of the spring 17.