Image forming apparatus

In an image forming apparatus, a plurality of cartridges each of which includes a photoconductor and a charger configured to charge the photoconductor is detachably installable in a main body housing. Chargers are connected in parallel to a voltage application unit configured to apply a voltage to the chargers. A cartridge installation determination unit is configured to determine whether or not each of the cartridges is installed. Control over the voltage application unit exercised by a controller includes a constant-voltage control and a constant-current control. The controller is configured to execute the constant-voltage control upon startup of an initial operation for preparation of printing and to switch from the constant-voltage control to the constant-current control if the cartridge installation determination unit determines that all the cartridges are installed.