PURPOSE: To provide a portable electric screw cutting machine which is capable of facilitating the screw cutting operation and a tap to be used therefor.

CONSTITUTION: A body is provided with a holding part and formed portable. A motor 4, a connector 5 and a tap 16 are arranged within this body 1. A guide male screw part 19 of the tap 16 is screwed with a guide female screw part 13a of a guide nut 13 provided to the body 1. When the motor 4 is rotated, the tap advances screwise. This tap 16 is provided with a rotational force receiving part 17 to receive the external rotational force (rotational force of the motor 4) at the base part, and a screwed part 18 at the tip part, and at the same time, provided with the guide male screw part 19 having the same lead as that of the screwed part 18 in the middle of the tap.