To solve a problem wherein an arm part of a spring seat laterally slides against a fly weight, abrasion advances, and an injection amount is in creased, when a vibration load becomes large by high compression and high driving accompanying strengthening of restriction of exhaust gas.

Weight reduction of the spring seat 11 is realized by press- molding a metal plate and force applied to the spring seat 11 (vibration load×mass) is inhibited to a small degree. As a result, the lateral sliding of the spring seat 11 is inhibited and the abrasion caused by the lateral sliding can be prevented. A cost of the spring seat 11 can be inhibited. When the arm part 13 is bent to an approximately vertical direction against a cylindrical part of a dish part 12, a base part α of the arm part 13 may be crushed. However, the crushing of the base part α is avoided by providing a removal part 12b on the dish part 12 and the spring seat 11 is further reduced in weight.