A supercharger drive device (1) for a combustion engine (E) includes a gear carrier shaft (6) operable to rotate in unison with a crankshaft (2) of the combustion engine (E), a high speed gear (8) and a low speed gear (10) provided in the gear carrier shaft (6), a drive shaft (14) of a supercharger (12) which is rotatable when coupled with either one of the high speed gear (8) and the low speed gear (10), a gear shifter (16) for selecting one of the high speed gear (8) and the low speed gear (10) for transmitting a motive force from the gear carrier shaft (6) to the drive shaft (14) through the selected one of the high and low speed gears (8) and (10), and a shifter drive unit (18) for actuating the gear shifter (16) in dependence on the rotational speed of the combustion engine (E).