Belt member, transfer unit incorporating same, image forming apparatus incorporating same, and method of evaluating same

A multi-layer endless belt member (201) with a high-resistance surface layer (201a, 201c, 201e) for use in an image forming apparatus (1). A volume resistivity thereof ranges from approximately 8.0 to approximately 11.0 in log[©·cm]. An amount of resistivity change of a first surface thereof is greater than an amount of resistivity change of a second surface thereof by 0.05 or greater in log [© / square], where the amount of resistivity change of the first surface indicates a difference between surface resistivity values measured after a given voltage is applied for 1 second and for 100 seconds on the first surface thereof and the amount of resistivity change of the second surface indicates a difference between surface resistivity values measured after a given voltage is applied for 1 second and for 100 seconds on the second surface thereof.