To provide a compact system for supplying a fuel to a marine vessel generator which can save a space, is low in cost and advantageous in maintenance.

This fuel supply system for the marine vessel generator which supplies fuel A or fuel B while switching uses the fuel supply motor pump of the generator as a common pump for fuel A and C. A fuel supply piping which connects a fuel A supply piping from a fuel A tank and a fuel C supply piping from a buffer tank so as to be switchable from one to the other by using a switch valve, is connected to the above fuel supply motor pump. Thereby, fuel A and C are supplied to the generator by the fuel supply motor pump while being switched.