An image forming apparatus includes a development device, an electrostatic transfer device, a stopping period measuring part, a driving period measuring part, a toner consumption amount measuring part, an environment measuring part and a transferring bias adjusting part. The driving period measuring part measures a driving period in which the development device is driven in order to form the toner image. The transferring bias adjusting part adjusts the transferring bias on the basis of the stopping period measured by the stopping period measuring part, the driving period measured by the driving period measuring part, the toner consumption amount measured by the toner consumption amount measuring part and the condition of the surrounding environment measured by the environment measuring part.