To provide an endless seamless belt made of polyimide that assures stable belt running properties even in different environments and does not suffer from warpage at the edge portion, its manufacturing method and an image-forming apparatus.

The endless seamless belt has a ratio (TD/MD) of a moisture-absorption linear expansion coefficient (TD) in the circumferential direction of a belt to a moisture-absorption linear expansion coefficient (MD) in the axis direction of the belt within the range of 0.9 moisture-absorption linear expansion coefficient ratio (TD/MD) 1.1, where the moisture-absorption linear expansion coefficient ratio is measured in measuring conditions of a high-humidity condition: 35C/85% (relative humidity) and in a low-humidity condition: 35C/35% (relative humidity).