PURPOSE: To secure a wide space, insofar as possible, on a rear floor panel in the rear of back seats by contriving the mounting position of an engine and a layout around the engine at a time when a driving system inclusive of the engine is mounted beneath the rear floor panel.

CONSTITUTION: This is a car driving device 20 to be installed beneath a rear floor panel 7 where a baggage space 5 is set up upwards, and in this constitution, an engine En and a transmission TM installed in a horizontal position each are set up respectively so as to make both respective output shafts 21 and 22 extend in the car width direction, and to make the output shafts of the transmission be situated in the rear more than the engine output shaft, or concentrically otherwise. With this constitution, a suspension cross-member 15 extending in the car width direction in parallel with both these output shafts is installed so as to have its longitudinal center line situated in the rear more than the output shaft of the transmission.