Evaporated fuel treatment device

An evaporated fuel treatment device including a cylindrical casing body, a granular adsorbent filled in the casing body, an air permeable member stacked on the granular adsorbent, a retainer member stacked on the air permeable member, and a tooth-shaped positioning retention mechanism disposed between an inner circumferential surface of the casing body and an outer circumferential surface of the retainer member. The tooth-shaped positioning retention mechanism allows the retainer member to hold the air permeable member in a compressively deformed state, enables positioning and retention of the retainer member in an optional position relative to the casing body in a pushing direction of the retainer member, and inhibits displacement of the retainer member in a removal direction of the retainer member.