To provide a governor mechanism of an engine which achieves simpification of a configuration and reduction in size and weight.

In the mechanism, an exhaust gas receiving plate 31 which is rockably supported along the exhaust gas flow opposed to exhaust gas flow flowing in the muffler body 21 and a biasing means 35 which biases the exhaust gas receiving plate 31 to the upstream side of the exhaust gas flow, are provided inside the muffler body 21 of an exhaust muffler 20 connected to an exhaust pipe 22 composing an exhaust passage of an engine 1. The mechanism is equipped with a governor lever 33 coupled to the exhaust gas receiving plate 31 to rock integrally therewith. Thereby, the engine rotation speed is adjusted by utilizing wind pressure of the exhaust gas flow varying in accordance with an engine rotation speed.