An output job in an image forming apparatus not connected to a network is managed. To accomplish this, an image forming apparatus in an image forming system includes an input unit which inputs document data stored in a recording medium, a verification unit which verifies the validity of the document data on the basis of verification information associated with the input document data, an output unit which forms and outputs an image on a print medium on the basis of the document data, and an output log storing control unit which, when it is determined that the document data is valid, stores, in the recording medium, output log information containing no output image, and when it is determined that the document data is invalid, stores output log information containing the output image in the recording medium.