An electric power tool comprising: a rechargeable battery; a motor; a detector (15, 16, 17, 23, 24, 25) configured to detect a parameter that affects a voltage drop of the rechargeable battery and output a detection signal corresponding to the detected parameter; a controller configured to receive the detection signal and generate a control signal in accordance with the detection signal; a power switching unit operated in accordance with the control signal from the controller to switch between a situation in which the rechargeable battery supplies electric power to the motor and a situation in which the rechargeable battery stops supplying electric power to the motor, and an activation switch configured to be switched on and off, wherein the electric power tool is activated when the activation switch is turned on, wherein the controller is configured to: control the power switching unit using a pulse width modulation control signal when the electric power tool is activated, the electric power tool being characterized in that the controller is configured to: set a duty ratio of the PWM control signal for a start-up period (t0-t10; t0-t01; t0-t11) in accordance with the detection signal of the detector (15, 16, 17, 23, 24, 25) corresponding to the parameter detected at a first time, which is when the activation switch is turned on, wherein the start-up period (t0-t10; t0-t01; t0-t11) is a period from the first time to a second time (t10; t01; t11) that is different from the first time, and set a duty ratio of the PWM control signal to 100% at the second time (t10; t01; t11). a rechargeable battery; a motor; a detector (15, 16, 17, 23, 24, 25) configured to detect a parameter that affects a voltage drop of the rechargeable battery and output a detection signal corresponding to the detected parameter; a controller configured to receive the detection signal and generate a control signal in accordance with the detection signal; a power switching unit operated in accordance with the control signal from the controller to switch between a situation in which the rechargeable battery supplies electric power to the motor and a situation in which the rechargeable battery stops supplying electric power to the motor, and an activation switch configured to be switched on and off, wherein the electric power tool is activated when the activation switch is turned on, wherein the controller is configured to: control the power switching unit using a pulse width modulation control signal when the electric power tool is activated, the electric power tool being characterized in that the controller is configured to: set a duty ratio of the PWM control signal for a start-up period (t0-t10; t0-t01; t0-t11) in accordance with the detection signal of the detector (15, 16, 17, 23, 24, 25) corresponding to the parameter detected at a first time, which is when the activation switch is turned on, wherein the start-up period (t0-t10; t0-t01; t0-t11) is a period from the first time to a second time (t10; t01; t11) that is different from the first time, and set a duty ratio of the PWM control signal to 100% at the second time (t10; t01; t11). control the power switching unit using a pulse width modulation control signal when the electric power tool is activated, the electric power tool being characterized in that the controller is configured to: set a duty ratio of the PWM control signal for a start-up period (t0-t10; t0-t01; t0-t11) in accordance with the detection signal of the detector (15, 16, 17, 23, 24, 25) corresponding to the parameter detected at a first time, which is when the activation switch is turned on, wherein the start-up period (t0-t10; t0-t01; t0-t11) is a period from the first time to a second time (t10; t01; t11) that is different from the first time, and set a duty ratio of the PWM control signal to 100% at the second time (t10; t01; t11). set a duty ratio of the PWM control signal for a start-up period (t0-t10; t0-t01; t0-t11) in accordance with the detection signal of the detector (15, 16, 17, 23, 24, 25) corresponding to the parameter detected at a first time, which is when the activation switch is turned on, wherein the start-up period (t0-t10; t0-t01; t0-t11) is a period from the first time to a second time (t10; t01; t11) that is different from the first time, and set a duty ratio of the PWM control signal to 100% at the second time (t10; t01; t11).