Clutch connection/disconnection detection system for single-cylinder engine

The invention detects with high accuracy the connection/disconnection of a clutch intermediately provided between a crankshaft of a single-cylinder engine and a power transmission means for transmitting the output of the crankshaft. To achieve this, the rotation variation coefficient of a crankshaft 7 is detected by a rotation variation coefficient detection means 16, and a decision means 17 decides the connection/disconnection of a clutch 11 by comparing the rotation variation coefficient detected by the rotation variation detection means 16 with a preliminarily determined threshold.