FUEL TANK

A fuel tank including a built-in component is provided. The built-in component includes: a carrier part being a rigid body including a plurality of engaging parts, and a plurality of struts each including an engageable part to be engaged with one of the engaging parts. The engageable part of the strut includes an upper contact surface and a lower contact surface, which are formed spaced apart from each other in a height direction. The engaging parts of the carrier part each includes a biasing part that, when the strut is engaged with the engaging part, enters a space between the upper contact surface and the lower contact surface and generates biasing forces in directions to move the upper contact surface and the lower contact surface away from each other.