To facilitate work for choke valves for obtaining continuous self- driving after starting an internal combustion engine when the internal combustion engine is started in straddle type water craft.

This intake system juxtaposes intake passages 20 capable of introducing air A into each cylinder of an internal combustion engine mounted on a hull. A fuel supply pipe 32 is provided to introduced fuel B in each intake passage 20. A choke valve 40 is provided to freely open and close the upstream part of each intake passage 20 rather than the fuel supply port 34 of each fuel supply pipe 32. Each choke valve 40 is provided with a communicating port 47 for communicating the upstream part of each intake passage 20 rather than each choke valve 40 with the downstream part when each choke valve 40 totally closes each intake passage 20. In the choke valves 40, the communicating port 47(A) of one choke valve 40(A) has an opening area larger than that of the communicating port 47(B) of the other choke valve 40(B).