A fuel supply structure in a vehicle engine having: an air cleaner comprising a cleaner case divided by a bulkhead holding a cleaner element into an unpurified chamber and a purified chamber, main fuel injection valves (66F, 66R) for injecting fuel into intake passages (57F, 57R) communicating between the purified chamber and intake ports (44F, 44R) provided in a cylinder head (32F, 32R) of an engine body, and secondary fuel injection valves (67F, 67R) for injecting fuel into the intake passages (57F, 57R) upstream of the main fuel injection valves (66F, 66R) in a flow direction in the intake passages (57F, 57R), wherein the secondary fuel injection valves (67F, 67R) are housed in the purified chamber, wherein the main fuel injection valves (66F, 66R) are housed in the unpurified chamber, wherein a common fuel supply conduit for leading fuel from a common fuel tank to the main fuel injection valves (66F, 66R) and to the secondary fuel injection valves (67F, 67R) is connected to a branching connection pipe which is supported to pass through the cleaner case and the bulkhead and the branch being placed in the unpurified chamber, and wherein the branching connection pipe is connected to a main fuel injection valve side branched fuel conduit for leading fuel toward the main fuel injection valves (66F, 66R) and to a secondary fuel injection valves side branched fuel conduit for leading fuel toward the secondary fuel injection valves (67F, 67R), wherein the branching connection pipe has a pair of branched pipe portions (81b, 81c) placed in the unpurified chamber and wherein one of both of the branched pipe portions (81b, 81c) passes through the bulkhead and is supported by the bulkhead to split on the purified chamber side for leading fuel to every secondary fuel injection valve (67F, 67R). an air cleaner comprising a cleaner case divided by a bulkhead holding a cleaner element into an unpurified chamber and a purified chamber, main fuel injection valves (66F, 66R) for injecting fuel into intake passages (57F, 57R) communicating between the purified chamber and intake ports (44F, 44R) provided in a cylinder head (32F, 32R) of an engine body, and secondary fuel injection valves (67F, 67R) for injecting fuel into the intake passages (57F, 57R) upstream of the main fuel injection valves (66F, 66R) in a flow direction in the intake passages (57F, 57R), wherein the secondary fuel injection valves (67F, 67R) are housed in the purified chamber, wherein the main fuel injection valves (66F, 66R) are housed in the unpurified chamber, wherein a common fuel supply conduit for leading fuel from a common fuel tank to the main fuel injection valves (66F, 66R) and to the secondary fuel injection valves (67F, 67R) is connected to a branching connection pipe which is supported to pass through the cleaner case and the bulkhead and the branch being placed in the unpurified chamber, and wherein the branching connection pipe is connected to a main fuel injection valve side branched fuel conduit for leading fuel toward the main fuel injection valves (66F, 66R) and to a secondary fuel injection valves side branched fuel conduit for leading fuel toward the secondary fuel injection valves (67F, 67R), wherein the branching connection pipe has a pair of branched pipe portions (81b, 81c) placed in the unpurified chamber and wherein one of both of the branched pipe portions (81b, 81c) passes through the bulkhead and is supported by the bulkhead to split on the purified chamber side for leading fuel to every secondary fuel injection valve (67F, 67R).