IMAGE FORMING APPARATUS

An image forming apparatus includes a plurality of image bearers, an intermediate transferor, a plurality of primary transferors, a primary transfer power source, a primary transfer current detector, and processing circuitry. The primary transferors primarily transfer toner images of colors from the image bearers onto the intermediate transferor. The intermediate transferor secondarily transfers the toner images onto a transfer medium. The primary transfer power source applies voltage to the primary transferors. The primary transfer current detector detects a current flowing through the primary transferors when a specified voltage is applied to the primary transferors and is connected to only one primary transferor of one color among all the colors. The processing circuitry determines a primary transfer voltage based on a current value detected by the primary transfer current detector and determines a primary transfer voltage value of the primary transferors of all the colors based on the detected current value.