To provide a cutting blade clutch for a riding mower enabled to disconnect the power of a mowing machine instantaneously in an emergency by disposing a clutch lever of the mowing machine directly under a steering wheel of an operator's seat of the riding mower. [Solution] A riding mower is provided with a clutch lever 12 for the cutting blade, the clutch lever 12 being disposed directly under a steering wheel 7 of the operator' s seat. Power is connected by lifting the clutch lever 12 and the power is disconnected by lowering the clutch lever 12. The clutch lever 12 is constituted of a U-shaped lever mounted below the steering wheel and which is freely rotatable in an up and down direction, the clutch lever 12 droops below the steering wheel 7 when the power is disconnected, and a tip of the U-shaped lever is positioned directly under an outer edge of the round steering wheel 7 on a side of the operator's seat when the power is connected.