An operation lever unit includes an operation handle attached to an operating rod of an engine-powered portable working machine. The operation handle is equipped with a throttle lever for regulating the power of an engine, a lock lever for holding the throttle lever in a desired position, and a secondary throttle adjustment lever for achieving a fine adjustment of the position of the throttle lever. To hold the throttle lever in the desired position, the throttle lever is forced against a portion of the operation handle by the action of a thrust cam mechanism disposed between the throttle lever and the lock lever. For achieving the fine adjustment of the throttle lever position, the secondary throttle adjustment lever is forced by a thumb of the operator to forcibly turn the throttle lever against a frictional force acting between the throttle lever and the handle portion.