A mixer drum driving apparatus includes an auxiliary fluid pressure pump that is provided independently of a fluid pressure pump and is capable of supplying a working fluid to a fluid pressure motor so as to cause a mixer drum to perform agitation rotation, a plurality of motors configured to drive the auxiliary fluid pressure pump to rotate, and a control unit that controls rotation of the mixer drum. When an engine is stopped during the agitation rotation of the mixer drum, the control unit drives the auxiliary fluid pressure pump to rotate by operating the plurality of motors selectively in accordance with a load of the mixer drum.