The objective of the present invention is to obtain a vehicle electric-power conversion apparatus in which high-efficiency rectification operation can be realized, by detecting in real time a change, due to a fluctuation in a load, in a phase at which a switching element is turned on/off and by changing the phase at which the switching element is turned on/off, in response to the change. A diode-on timing and a diode-off timing corresponding to the diode conduction state of a diode connected in parallel with a switching element are detected; the values of rotor-position signals corresponding to the timings are sequentially stored; based on the stored values of rotor-position signals, a switching-element-on timing and a switching-element-off timing are calculated; and based on the timings, a gate command signal for the switching element is created.