An electric exercise spotting device for assisting muscular strength exercises, provided with a safety bar driven by a motor for exercise spotting, the electric exercise spotting, device characterized in that said electric exercise spotting device comprises: sensors comprising a first sensor for detecting the number of times of exercise and an exercise speed, and a second sensor for detecting that the safety bar approaches an object; the motor, driven by a control signal, for generating an external force and transmitting an encoder signal; a microcomputer for deriving calculation values of an exercise spotting point, an exercise spotting intensity, and an exercise spotting position on the basis of user information and an exercise intensity, the number of times of exercise and an exercise speed detected by the first sensor, and an encoder signal by correcting a driving frictional force inside the exercise spotting device, for calculating an external force value to be generated by the motor based on the calculation values, and for sending out the control signal to the motor; a mount detachably attached to a vertical frame of a rack used for the muscular strength exercises; a base rail, fixed parallel to the mount, for guiding movement of the safety bar; a power transmission unit, positioned inside the base rail, for transmitting the power of the motor to the safety bar; the safety bar for application of the external force, which is required for exercise spotting and exercise, by receiving the power generated from the motor, and for enabling detachment and attachment of a barbell bar for the muscular strength exercises; and a rest, fixed to the mount or the base rail in a locking manner, for resting heavy weights, used for the muscular strength exercises, at an exercise starting position; wherein the mount comprises a rod-shaped mounting pin which is installed through the vertical frame of the rack used for the muscular strength exercises; a first mount in the shape of a U-beam provided with a first locking groove with which the mounting pin is engaged and a rest groove with which the rest is engaged; and a second mount in the shape of a U-beam to which the base rail is fixed and provided with a second locking groove with which the mounting pin is engaged. sensors comprising a first sensor for detecting the number of times of exercise and an exercise speed, and a second sensor for detecting that the safety bar approaches an object; the motor, driven by a control signal, for generating an external force and transmitting an encoder signal; a microcomputer for deriving calculation values of an exercise spotting point, an exercise spotting intensity, and an exercise spotting position on the basis of user information and an exercise intensity, the number of times of exercise and an exercise speed detected by the first sensor, and an encoder signal by correcting a driving frictional force inside the exercise spotting device, for calculating an external force value to be generated by the motor based on the calculation values, and for sending out the control signal to the motor; a mount detachably attached to a vertical frame of a rack used for the muscular strength exercises; a base rail, fixed parallel to the mount, for guiding movement of the safety bar; a power transmission unit, positioned inside the base rail, for transmitting the power of the motor to the safety bar; the safety bar for application of the external force, which is required for exercise spotting and exercise, by receiving the power generated from the motor, and for enabling detachment and attachment of a barbell bar for the muscular strength exercises; and a rest, fixed to the mount or the base rail in a locking manner, for resting heavy weights, used for the muscular strength exercises, at an exercise starting position; wherein the mount comprises a rod-shaped mounting pin which is installed through the vertical frame of the rack used for the muscular strength exercises; a first mount in the shape of a U-beam provided with a first locking groove with which the mounting pin is engaged and a rest groove with which the rest is engaged; and a second mount in the shape of a U-beam to which the base rail is fixed and provided with a second locking groove with which the mounting pin is engaged.