In an image forming apparatus having an image forming portion for forming an image on an image bearing member, a transferring portion provided with a transferring member capable of contacting with the image bearing member and a voltage applying portion for applying a voltage to the transferring member, and for electrostatically transferring the image on the image bearing member to a transferring medium, an electric current detecting portion for detecting an electric current flowing to the transferring member, and a control portion for performing an electric current detecting operation of detecting an electric current flowing when the voltage applying portion applies a predetermined voltage before an image transferring operation by the electric current detecting portion, and determining a transfer voltage applied to the transferring member during the image transferring operation on the basis of a result of the detection by the electric current detecting operation, the electric current detecting operation is performed a plurality of times, and a time required for an electric current detecting operation performed before a certain electric current detecting operation performed at and after the second time is shorter than a time required for the certain electric current detecting operation.