PURPOSE: To make it possible to select an adequate compression ratio and an ignition timing constantly responding to the sort of fuel, and to improve the engine output, by making it possible to set the compression ratio and the basic ignition timing responding to the selected fuel of the two sorts of fuel.

CONSTITUTION: The first and the second fuel feeding devices are provided to feed two kinds of fuel of different characters (gasoline and a compressed natural gas, for example) to an engine at a specific amount responding to the operational condition, and they are operated selectively by a feeding fuel converting device 4. Responding to the fuel selected by the converting device 4, the compression ratio of the engine is set by a compression variable device 5, and depending on the selected fuel, at the same time, the basic ignition timing is set by the first and the second ignition timing setting devices 3a and 3b. A compressed natural gas fuel control circuit 61 and a gasoline fuel control circuit 62 are composed by ignition timing setting devices 3a and 3b, and the first and the second air-fuel ratio setting devices to control the fuel feeding devices 1 and 2 respectively.