A driver comprising: a battery; a wheel rotationally driven by an electric motor using the battery as a power source; an engaging part provided to the wheel and arranged along a circumferential direction of the wheel; a piston reciprocably housed in a cylinder; a driver blade integrally reciprocating with the piston; a plurality of racks provided to the driver blade along an axial direction of the driver blade; characterized by a controller configured to control a drive of the electric motor, wherein when the wheel is rotationally driven, the engaging part and the racks are sequentially engaged with each other so as to push up the driver blade, and when the piston moves from a bottom dead point side to a top dead point side in the cylinder, and when the engaging part is disengaged from the racks, the piston moves from the top dead point side to the bottom dead point side in the cylinder, and the driver blade moves down, wherein the controller is further configured to control a switching element (Q1-Q6) provided on a power supply line for the electric motor by PWM, the controller is further configured to control the electric motor in response to a remaining battery level so as to suppress variation between a time required from the start of the electric motor until the piston starts to move toward the bottom dead point when the remaining battery level is smaller than a reference value, and a time required from the start of the electric motor until the piston starts to move toward the bottom dead point when the remaining battery level is larger than the reference value, the controller has first and second starting modes as a control mode for the electric motor, wherein in the first starting mode, a duty ratio at the time of starting the electric motor is a first value, and in the second starting mode, the duty ratio at the time of starting the electric motor is a second value higher than the first value, and the controller is configured to start the electric motor in the first starting mode when the remaining battery level is larger than the reference value, and start the electric motor in the second starting mode when the remaining battery level is smaller than the reference value. a battery; a wheel rotationally driven by an electric motor using the battery as a power source; an engaging part provided to the wheel and arranged along a circumferential direction of the wheel; a piston reciprocably housed in a cylinder; a driver blade integrally reciprocating with the piston; a plurality of racks provided to the driver blade along an axial direction of the driver blade; characterized by a controller configured to control a drive of the electric motor, wherein when the wheel is rotationally driven, the engaging part and the racks are sequentially engaged with each other so as to push up the driver blade, and when the piston moves from a bottom dead point side to a top dead point side in the cylinder, and when the engaging part is disengaged from the racks, the piston moves from the top dead point side to the bottom dead point side in the cylinder, and the driver blade moves down, wherein the controller is further configured to control a switching element (Q1-Q6) provided on a power supply line for the electric motor by PWM, the controller is further configured to control the electric motor in response to a remaining battery level so as to suppress variation between a time required from the start of the electric motor until the piston starts to move toward the bottom dead point when the remaining battery level is smaller than a reference value, and a time required from the start of the electric motor until the piston starts to move toward the bottom dead point when the remaining battery level is larger than the reference value, the controller has first and second starting modes as a control mode for the electric motor, wherein in the first starting mode, a duty ratio at the time of starting the electric motor is a first value, and in the second starting mode, the duty ratio at the time of starting the electric motor is a second value higher than the first value, and the controller is configured to start the electric motor in the first starting mode when the remaining battery level is larger than the reference value, and start the electric motor in the second starting mode when the remaining battery level is smaller than the reference value.