A fuel supply device includes a cover, a base including a base main body, and a connecting portion configured to connect the cover and the base. The base main body and the connecting portion are connected by a connecting shaft comprising a shaft portion and a bulge portion, a connecting hole formed so as to continuously extend an engagement region and an insertion region, and a stopper piece capable of limiting a movable range of the shaft portion located within the engagement region towards the insertion region. A guide mechanism is provided for guiding the connecting shaft to move so that at least one part of the stopper piece is positioned between the bulge portion and the base portion when a predetermined amount of force is applied to the connecting shaft.