PURPOSE: To restrain the emission of yellow smoke and the like from a dual fuel engine by externally placing liquid fuel torch cells for igniting a fuel mixture under an optimum state.

CONSTITUTION: In a dual fuel engine having an inlet valve, an exhaust valve, and a first liquid fuel injection device 40 at a cylinder head 24, two torch cells 50 are arranged externally. The torch cell 50 comprises a second fuel injection device 80 and an auto-ignition chamber 100, which is communicated with a main cylinder chamber 1 7 via a torch nozzle passage 102. Therefore, a fuel mixture flowing into the automatic ignition chamber 100 from the torch nozzle passage 102 near the compressive top dead center of a piston 22 is ignited under an optimum state by the fuel injected from the fuel injection device 80. Thus, emission of yellow smoke and other exhaust gases in a dual fuel mode can be controlled.