A switching circuit for varying rotational speed of a motor includes a power supply line for connecting the motor to a power source so as to supply driving power to the motor. A parallel connecting circuit of an on-off switch and a short circuiting switch is provided in the power supply line, in such a manner that the driving power is continuously supplied to the motor when the short circuiting switch is on, while in the case that the short circuiting switch is off, the driving power is supplied to the motor during on of the on-off switch but is not supplied during off of the on-off switch. A control member is provided for operation by an operator for varying rotational speed of the motor. The control member is operative for turning on the short circuiting switch at the maximum amount of its operation. The switching circuit further includes an output element for producing an output signal corresponding to the amount of operation of the control member, a continuously conductive switch to be continuously kept on when the control member is operated between the maximum amount of operation and the amount slightly smaller than the maximum amount, and a control element connected to the output element and the continuously conductive switch for controlling the on-off switch.