PURPOSE: To perform a developing process stably without interrupting the process owing to the too large or too small amount of a liquid developer by measuring the area of an optional density area by a photosensor from a developed body after development and correcting the too large or too small replenishing amount of the device.

CONSTITUTION: A photosensitive material is mounted on a conveyor belt 1, passed through a photosensitive width reader 2, and sent to a developing rack 4 in a developing tank 3, the photosensitive material width reader and sends the conveyance quantity of the photosensitive material to an arithmetic control part to obtain a specific quantity, and standard replenishing is started. The head part of the photosensitive material exits from a developing tank, advances to a next processing tank, and passes between light shield covers 5 to reach a light room processing process. The photosensitive material passes through the photosensor 6 and advances to a next process and the photosensor measures the optional density area quantity from the image density of the photosensitive material to obtain data. Those data are sent to the arithmetic control part and compared with the data read by the photosensitive material width reader and when the replenishing quantity is too larger or too small, a replenishment driving part is controlled to maintain a proper replenishing quantity. Consequently, the liquid developer is supplied finely and a stable developing process is performed.