PURPOSE: To prevent a tank part from being moved on a holder in traveling of a vehicle, place the tank part on the holder with good stability, accurately position it, and omit the deburring process of the tank part.

CONSTITUTION: In a holding structure of a tank part constituted by placing a resin-molded tank part 16 on a holder 23 formed into a pan shape, so as to regulate the movement of the tank part 16 an engaging projecting part 26 is projectingly provided on the front surface of the tank part 16, and an engaging recessed part 27 with which the engaging projecting part 26 can be engaged is provided on the holder 23 side. A flange-like burr to be formed on the front surface in molding of the tank part 16 is utilized as the engaging projecting part 26, and the engaging recessed part 27 is formed into a shape of a groove with which the burr can be engaged.