PURPOSE: To save fuel at the time of partial-load operation of a multi-cylinder engine compressor, by stopping pumping action of part of cylinders of a compressor, and at the same time stopping ignition of part of cylinders of the engine.

CONSTITUTION: A multi-cylinder engine compressor comprises an engine 2, a compressor 3 and a control unit 4. At the time of full-load operation of the apparatus, a control circuit 7 does not give an ignition stopping instruction nor an operation cancelling instruction to any of cylinders 21W26, 31W36, so that all of the cylinders are operated at phase intervals of 120°. At the time of half- load operation of the apparatus, on the other hand, the cycle time of one operation cycle of the cylinders 21W26 is made twice as long as that of one operation cycle at the time of full-load operation. While the apparatus operates 1,440°, ignition and pumping action are effected in a predetermined sequence by producing ignition stopping instruction and operation cancelling instruction. At the time of other partial-load operation, ignition and pumping action are effected in a predetermined sequence. Thus, it is enabled to save fuel for the cylinders of engine which are in rest state.