An image forming apparatus includes a storage part storing a plurality of job data, an output part outputting a job of the job data and a job data erasion controlling part configured to overwrite and delete a previously output job data output from the output part. The job data erasion controlling part overwrites and deletes the previously output job data in an idle time other than a time at which the storage part is read and/or written when the job is output, and then, if the storage part has a free space area having a capacity larger than a predetermined capacity, the output job data is overwritten and deleted in descending order of data size, and if the storage part has a free space area having a capacity smaller than the predetermined capacity, the output job data is overwritten and deleted in ascending order of data size.