In a hybrid vehicle in which a fixed speed change mode can be realized by the locking of a rotational element, the mislocking of the rotational element is prevented. A hybrid drive apparatus which has an engine, a MG1 and a MG2 and which functions as a power unit of a hybrid vehicle is provided with a brake mechanism of a cam-lock type which can control the MG1 in a lock state and a non-lock state by changing the state of a sun gear between the lock state and the non-lock state. In mislocking prevention control, an ECU calculates MG1 angular acceleration Dωg, which is the absolute value of angular acceleration of the motor generator MG1, on the basis of a MG1 rotational speed Ngm1 and judges that the sun gear S1 is in a mislocking state if the MG1 angular acceleration Dωg is greater than a criterion value Dωgth.