PURPOSE: To reduce the manufacturing cost and manufacturing time of a fuel tank and increase tank capacity.

CONSTITUTION: As for a fuel tank 26 for a motorcycle which is constituted by joining a tank inner 28 having a recessed part 29 formed at the center part and a tank outer 28 having an inlet 30 installed at the top part and closing the inlet 30 by a tank cap 31, a separator 36 which achieves the air/liquid separating function is accommodated into the fuel tank 26, and the inlet 36 is extended toweard the recessed part 29 of the tank inner 28, and a recessed part 48 recessed in the direction separating from the inlet 30 is formed at the part corresponding to the inlet 30 of the recessed part 29.