To provide a bi-fuel engine for a vehicle, which restrains transmission of both of actuation noise of a gas fuel injection valve and actuation noise of a liquid fuel injection valve to a vehicle compartment while maintaining good maintainability of a gas fuel injection unit, and which can protect the gas fuel injection valve.

A surge tank 52 is placed above an engine body 4. A plurality of intake branch pipes 51 include curved portions 51C which are placed on a side part of the engine body 4, and sloped portions 51D inclining downward from the surge tank 52 toward 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 body 4 and the intake branch pipes 51. A gas fuel injection unit 11 is placed in a gap between the surge tank 52 and the air cleaner 7. Gas fuel injection valves 10B are held by a bracket 30 on a gas fuel delivery pipe 10A so that they are placed below the air cleaner 7 in a space between the sloped portions 51D adjacent to each other.