A belt unit includes an endless belt and a cleaning member. The endless belt has a value of ten-point height of roughness Rz not larger than 0.2 .mu.m, a value of shininess not less than 100, a creep not larger than 0.03%. The cleaning member is in contact with said endless belt and removes foreign matter adhering to said endless belt. The belt unit may be applied to an image forming apparatus either of direct transfer type and intermediate transfer type.