Abstract: A fuel filler cap canister for a fuel filler cap includes: a base part having an attachment section attached to the cap and a communicating hole communicating with a fuel tank and formed in the base part; and a case member assembled to the base part and having an inner volumetric space provided with a spiral rib. The spiral rib extends from an opposing face of the case member facing the base part or an opposing face of the base part facing the case member toward the base part or the case member, respectively, and forms an adsorption path connecting the communicating hole and an atmosphere communicating hole formed in either one of a vicinity of a peripheral edge or substantially a central portion of the opposing face of the case member facing the base part. The adsorption path is filled with an adsorbing device.