Fuel tank and straddle-type vehicle

A fuel tank (7) has a tank body (71), a tank filler (72) formed in a tubular shape, and a flame arrestor (73) formed in a calathiform. The tank filler has a first opening (72S) and a second opening (72T). The flame arrester is attached to the tank filler so as to cover the second opening. The inner diameter of the flame arrester is smaller than the inner diameter of the tank filler.