A gear mounting structure for a fishing reel includes a screw shaft, a gear component and a ring member. The screw shaft has a shaft body, a spiral groove and a mounting part provided at an end of the shaft body. The spiral groove has a crossing point on an exterior circumference of the shaft body. The gear component has a gear body, a plurality of gear teeth and a mounting cavity. The gear teeth are formed in a circumferential direction along an exterior circumference of the gear body. The mounting cavity is for non-rotatably mounting the mounting part. The ring member has an elastic body interposed between the mounting part and the mounting cavity.