An image forming apparatus is provided, which enables various kinds of drive in accordance with purposes. The image forming apparatus includes photoelectric conversion elements and TFT units which are arranged in a matrix shape, a signal processing circuit unit (for processing a signal from each photoelectric conversion element, and a gate driver circuit unit for controlling connections among the photoelectric conversion elements. The gate driver circuit unit is connected to the TFT units through gate lines. The gate lines include one that is connected to the TFT units in each row, and the gate lines include one that is connected to the TFT units in plural rows.