A mounting structure for a heat accumulation tank is provided with an elastic member that wraps around a tank main body, and a heat accumulation tank mounting member which wraps around the outer peripheral surface of the elastic member and holds the tank main body by being tightened in the circumferential direction, and which attaches to a receiving member. The elastic member is a molded part. The length of the elastic member is shorter than length of the circumference of the outer peripheral surface of the tank main body. The heat accumulation tank mounting member includes a shift inhibiting portion which inhibits an upward shift of the tank main body. The outside diameter of the tank main body becomes increasingly wider in the upward direction.