A shock absorber includes an expansion-side passage and a contraction-side passage arranged alternately side by side along a circumferential direction, seats provided to surround an outlet port of the expansion-side passage or an outlet port of the contraction-side passage, and valve bodies. The seats has an arc-shaped outer seat portion, middle seat portions extending from respective both ends in a circumferential direction of the outer seat portion toward a center axis side of the piston, and an inner seat portion extending from center axis side ends of the middle seat portions oppositely to the outer seat portion side in a circumferential direction to connect the neighboring middle seat portions. The inner seat portion is placed on a straight line that connects the center axis side ends of the middle seat portions.