The fuel filler neck device is attached to a filler pipe and is opened and closed by a fueling nozzle. The device has a cover member which has an introduction opening for the fueling nozzle and which is engaged with the filler pipe side with engagement parts formed on the filler pipe side being fitted in window holes. Insertion parts are respectively formed adjacent to the engagement parts in the circumferential direction of the filler pipe. The engagement parts can be each disengaged by deforming or breaking the cover member side by inserting a portion of a tool into the insertion part.