The organic thin film photovoltaic device with a structure of tin indium oxide (ITO)/organic semiconductor/metal is fabricated. A rectifying behavior of the device is observed from the current-voltage characteristics. However, it is hard to judge the direction of internal electric field between the organic semiconductor and electrodes under Schottky contacts. In order to investigate the characteristics of Schottky contacts between the organic semiconductor and electrodes, the devices with the structures of ITO/organic insulator layer/organic semiconductor/metal and ITO/organic semiconductor/organic insulator layer/metal are fabricated. It is easy to judge the direction of internal electric field between the organic semiconductor and electrodes under Schottky contacts by the direction of transient photocurrent which is produced under the irradiation from the modulated laser. The correctness of judgement is further proved by the change of transient photocurrent intensity with a bias voltage applied.