A belt assembly includes a belt, a plurality of support rollers, and a shaft-end retainer. The belt is formed into an endless loop, entrained about and stretched taut between the plurality of support rollers with a rotary shaft. The plurality of support rollers includes a first support roller and a second support roller. The shaft-end retainer including a first retainer and a second retainer is disposed at each end of the rotary shaft of the plurality of support rollers. The first retainer detachably holds an end of the rotary shaft of the first support roller. The second retainer detachably holds an end of the rotary shaft of the second support roller and includes a second-retainer opening from which the end of the rotary shaft of the second roller is detachable from and attachable to the second retainer in a direction perpendicular to the rotary shaft of the second support roller.