A rotating electric machine with a built-in control device that can be downsized. The rotating electric machine with a built-in control device includes a rotor including a permanent magnet of sensor use provided on a rear side of a rotor shaft, a front side housing fixed with a first bearing supporting a front side of the rotor shaft, a motor frame including a rotor and a stator, a heat sink fixed with a second bearing supporting the rear side of the rotor shaft, a control substrate mounting a rotary sensor, a microcomputer, and a driving circuit. The microcomputer controls the driving circuit based on signals from the rotary sensor and drives a plurality of switching elements. At least one of a smoothing condenser and a noise reduction coil, connected to the switching elements, is arranged at a far rear side of the control substrate.