An electric motor control apparatus that controls an electric motor system, the electric motor system having: a DC (Direct Current) power source; an electrical power converter that converts DC electrical power supplied from the DC power source to AC (Alternate Current) electrical power; a smoothing condenser that is connected electrically in parallel to the electrical power converter; and a three-phase AC electric motor that operates by using the AC electrical power outputted from the electrical power converter, the electric motor control apparatus comprising: a generating device (155u, 156v, 156w) that generates modulation signal (Vmu, Vmv, Vmw) by adding third harmonic signal to phase voltage command signal (Vu, Vv, Vw) that determines operation of the three-phase AC electric motor; and a controlling device that controls the operation of the electrical power converter by using the modulation signal on the basis of a magnitude relation between the modulation signal (Vmu, Vmv, Vmw) and carrier signal having predetermined frequency, characterized in that the electric motor control apparatus further comprises an adjusting device that adjusts amplitude of the third harmonic signal, if an absolute value of signal level of the modulation signal in each of two of three phases is larger than an absolute value of a peak value of the carrier signal, the adjusting device adjusting the amplitude of the third harmonic signal to make a peak value of voltage between terminals of the smoothing condenser in the case where the amplitude of the third harmonic signal is adjusted to be smaller than a peak value of the voltage between the terminals in the case where the amplitude of the third harmonic signal is not adjusted. a DC (Direct Current) power source; an electrical power converter that converts DC electrical power supplied from the DC power source to AC (Alternate Current) electrical power; a smoothing condenser that is connected electrically in parallel to the electrical power converter; and a three-phase AC electric motor that operates by using the AC electrical power outputted from the electrical power converter, a generating device (155u, 156v, 156w) that generates modulation signal (Vmu, Vmv, Vmw) by adding third harmonic signal to phase voltage command signal (Vu, Vv, Vw) that determines operation of the three-phase AC electric motor; and a controlling device that controls the operation of the electrical power converter by using the modulation signal on the basis of a magnitude relation between the modulation signal (Vmu, Vmv, Vmw) and carrier signal having predetermined frequency, characterized in that the electric motor control apparatus further comprises an adjusting device that adjusts amplitude of the third harmonic signal, if an absolute value of signal level of the modulation signal in each of two of three phases is larger than an absolute value of a peak value of the carrier signal, the adjusting device adjusting the amplitude of the third harmonic signal to make a peak value of voltage between terminals of the smoothing condenser in the case where the amplitude of the third harmonic signal is adjusted to be smaller than a peak value of the voltage between the terminals in the case where the amplitude of the third harmonic signal is not adjusted.