A hybrid vehicle driving system 1 of the invention includes a cylinder deactivated operation necessity determination unit for determining the necessity of a cylinder deactivated operation of an engine 6 when a required driving force required on a vehicle is smaller than a driving force of the engine 6 that runs in the cylinder deactivated operation. When the cylinder deactivated operation is determined to be unnecessary by the cylinder deactivated operation necessity determination unit, the vehicle can be driven in an EV driving by disengaging a first clutch 41 and a second clutch 42, whereas when the cylinder deactivated operation is determined to be necessary by the cylinder deactivated operation necessity determination unit, the engine 6 runs in the cylinder deactivated operation and at least one of the first clutch 42 and the second clutch 42 is engaged.