PURPOSE: To increase the fuel oil filling quantity and improve oil filling workability and the removing-fitting workability of a filler cap.

CONSTITUTION: The movable tube 7 of a filler tube 5 is formed in such a way as to be pushed out by a coil spring 11 into an oil filling position where an oil filler port 8 protrudes outside from an oil filling window 2, and the movable tube 7 is fixed into the oil filling position by lock mechanism 15 formed of a link 16 and a stopper 17. At the closing time of a filler lid 4, lock is released by lock release mechanism 26 formed of a lid retainer 28 and an arm part 27 extended from the stopper 17, and the movable tube 7 is reset into a storage position in a vessel 3 by tube push mechanism 29 formed in such a way as to push the upper edge of the link 16 by the lid retainer 28.