A working machine has a machine body, a working unit attached to the machine body, an internal combustion engine for driving the working unit, a traveling unit mounted on the machine body 11 for displacing the working unit over a ground surface to perform a work operation on the ground surface, and an electric motor for driving the traveling unit. A battery supplies electric power to the electric motor in a battery mode of the working machine to thereby drive the electric motor. A battery mode switch switches between an ON position in which the working machine is in the battery mode and an OFF position in which the working machine is not in the battery mode. A power generator is driven by the internal combustion engine to supply electric power to the battery and to the electric motor. A control unit controls rotation of the electric motor and shifts the working machine to the battery mode in accordance with an ON position of the battery mode switch so that the electric motor is driven only by electric power supplied by the battery while the internal combustion engine is maintained deactivated.