To provide a structure preventing large moment from being applied to a handle and a cage even if stopping an engine in a hand guide type trowel or cutting off driving torque to a rotor of the trowel.

A brake responding automatically to the cessation of drive torque delivery to the rotor is allowed to cooperate with a drive gear train of the concrete finishing trowel. The brake responding to reaction forces when applying the drive torque to the rotor is mounted to a worm shaft or a related component in a gearbox. The component shifts axially in one direction to release the brake in the presence of the reaction forces and shifts axially in an opposite direction in the absence of the reaction forces to apply the brake. Since this system is engaged and released fully automatically, it does not interfere with an operator's ability to steer or operate a machine.