A surge tank 52 is placed above an engine main body 4. Plural intake runners 51 include curved portions 51C, respectively, which are placed on one side of the engine main body 4, and sloped portions 51D extending from the surge tank 52 to the curved portions 51C. An air cleaner 7 is placed above the sloped portions 51D. A liquid fuel injection unit 8 is placed in a space between the engine main body 4 and the intake runners 51. A gaseous fuel injection unit 11 is placed in a gap between the surge tank 52 and the air cleaner 7. Gaseous fuel injection valves 103 are held by a bracket on a gaseous fuel delivery pipe 10A in a way that they are placed under the air cleaner, each of them being placed in a space between the adjacent two of the sloped portions 51D.