Working vehicle driven by a hydraulic actuator, comprising: - a hydraulic pump that outputs hydraulic oil for operating the hydraulic actuator; - an electric motor that drives the hydraulic pump; - a main battery that supplies direct current electric power; - an inverter that operates the electric motor by converting the direct current electric power from the main battery into alternating current electric power and supplying the alternating current electric power to the electric motor; - an electric motor relay that makes and breaks the connection between the main battery and the inverter; - a controller which is operated by direct current electric power from the main battery; and which controls the operation of the hydraulic actuator and the inverter, and makes and breaks the connection between the main battery and the inverter in use of the electric motor relay; - a controller relay that makes and breaks the connection between the main battery and the controller; - a power source monitoring controller that monitors the state of the main battery; and that makes and breaks the connection between the main battery and the controller in use of the controller relay; - a backup battery that supplies electric power to the power source monitoring controller; and - a key switch that makes and breaks the connection between the power source monitoring controller and the backup battery; wherein configuration is employed to execute: - when the power source monitoring controller and the backup battery are connected by the key switch and the power source monitoring controller is operating, - - a first step in which the power source monitoring controller obtains the state of the main battery and determines whether the main battery can be used or not; - - a second step in which the power source monitoring controller connects the main battery and the controller in use of the controller relay and starts up the controller when judgment is made in the first step that the main battery can be used; and - - a third step in which the controller starts the electric motor by connecting the inverter and the main battery in use of the electric motor relay. - a hydraulic pump that outputs hydraulic oil for operating the hydraulic actuator; - an electric motor that drives the hydraulic pump; - a main battery that supplies direct current electric power; - an inverter that operates the electric motor by converting the direct current electric power from the main battery into alternating current electric power and supplying the alternating current electric power to the electric motor; - an electric motor relay that makes and breaks the connection between the main battery and the inverter; - a controller which is operated by direct current electric power from the main battery; and which controls the operation of the hydraulic actuator and the inverter, and makes and breaks the connection between the main battery and the inverter in use of the electric motor relay; - a controller relay that makes and breaks the connection between the main battery and the controller; - a power source monitoring controller that monitors the state of the main battery; and that makes and breaks the connection between the main battery and the controller in use of the controller relay; - a backup battery that supplies electric power to the power source monitoring controller; and - a key switch that makes and breaks the connection between the power source monitoring controller and the backup battery; wherein configuration is employed to execute: - when the power source monitoring controller and the backup battery are connected by the key switch and the power source monitoring controller is operating, - - a first step in which the power source monitoring controller obtains the state of the main battery and determines whether the main battery can be used or not; - - a second step in which the power source monitoring controller connects the main battery and the controller in use of the controller relay and starts up the controller when judgment is made in the first step that the main battery can be used; and - - a third step in which the controller starts the electric motor by connecting the inverter and the main battery in use of the electric motor relay. - when the power source monitoring controller and the backup battery are connected by the key switch and the power source monitoring controller is operating, - - a first step in which the power source monitoring controller obtains the state of the main battery and determines whether the main battery can be used or not; - - a second step in which the power source monitoring controller connects the main battery and the controller in use of the controller relay and starts up the controller when judgment is made in the first step that the main battery can be used; and - - a third step in which the controller starts the electric motor by connecting the inverter and the main battery in use of the electric motor relay. - - a first step in which the power source monitoring controller obtains the state of the main battery and determines whether the main battery can be used or not; - - a second step in which the power source monitoring controller connects the main battery and the controller in use of the controller relay and starts up the controller when judgment is made in the first step that the main battery can be used; and - - a third step in which the controller starts the electric motor by connecting the inverter and the main battery in use of the electric motor relay.