A portable drilling machine wherein when a shorting failure occurs in a circuit part connected to a driving motor, this state is reliably detected and a false start of the motor is reliably prevented. A diving motor control circuit in the portable drilling machine includes a main control section; a triac and a relay which are connected to power supply terminals in series with the driving motor; peripheral circuits (a triac control circuit, a relay control circuit, a triac inspection and determination section, a bypass resistor, etc.) which are related to the triac and relay; and a current measurement section for measuring current flowing in the driving motor.