Provided is an easy-to-use electric tool with which braking force can be changed according to work conditions. When an operation switch 5 is turned off, a control unit 50 detects a rotation rate R1 of an electric motor 6. The control unit 50 stands by for a prescribed period, detects a rotation rate R2 of the electric motor 6, and calculates the difference between the rotation rates R1, R2 (R=R1−R2). Since the rotation rate difference R corresponds to the rate of change in rotation rate with time during deceleration of the electric motor 6 and is smaller the larger the moment of inertia of the attached rotary tool, the control unit 50 can determine the moment of inertia of the rotary tool on the basis of the rotation rate difference R. The control unit 50 sets the braking force according to the moment of inertia and performs braking.