An image forming apparatus including: a photosensitive drum having a surface on which an electrostatic latent image is formed while the surface rotates in a circumferential direction of the photosensitive drum; a charging section configured to charge the surface of the photosensitive drum; an exposure section configured to irradiate the surface of the photosensitive drum charged by the charging section with light to form the electrostatic latent image; a developing section configured to supply toner to the electrostatic latent image formed on the surface of the photosensitive drum by the exposure section to form a toner image; a transfer roller having ion-conductivity and configured to transfer the toner image from the surface of the photosensitive drum to a recording medium using a transfer bias; a transfer bias applying section configured to apply to the transfer roller the transfer bias of reverse polarity to charge of the toner forming the toner image; a conveyance section configured to, during single-sided printing, successively convey a plurality of the recording media to a toner image transfer position for transfer of the toner image located between the photosensitive drum and the transfer roller and, during double-sided printing, successively convey a plurality of the recording media by reversing the recording medium having once passed through the toner image transfer position and conveying the reversed recording medium to the toner image transfer position again; and a control section configured to, in the case of causing the conveyance section to convey the recording medium during double-sided printing, cause the transfer bias applying section to apply the transfer bias to the transfer roller while the recording medium passes through the toner image transfer position and then cause the transfer bias applying section to apply a reverse bias of the same polarity as the charge of the toner to the transfer roller during a period from the time when the recording medium has passed through the toner image transfer position to the time when the recording medium is conveyed again to the toner image transfer position after being reversed, characterized in that the control section is configured to perform, after the completion of the single-sided printing or the double-sided printing, a post-aging, by causing the transfer bias applying section to apply the reverse bias to the transfer roller, and, to calculate an execution time for the post-aging so that the ratio of a total time of application of the reverse bias performed by the image forming apparatus to a total time of application of the transfer bias performed by the image forming apparatus is a predetermined ratio. a photosensitive drum having a surface on which an electrostatic latent image is formed while the surface rotates in a circumferential direction of the photosensitive drum; a charging section configured to charge the surface of the photosensitive drum; an exposure section configured to irradiate the surface of the photosensitive drum charged by the charging section with light to form the electrostatic latent image; a developing section configured to supply toner to the electrostatic latent image formed on the surface of the photosensitive drum by the exposure section to form a toner image; a transfer roller having ion-conductivity and configured to transfer the toner image from the surface of the photosensitive drum to a recording medium using a transfer bias; a transfer bias applying section configured to apply to the transfer roller the transfer bias of reverse polarity to charge of the toner forming the toner image; a conveyance section configured to, during single-sided printing, successively convey a plurality of the recording media to a toner image transfer position for transfer of the toner image located between the photosensitive drum and the transfer roller and, during double-sided printing, successively convey a plurality of the recording media by reversing the recording medium having once passed through the toner image transfer position and conveying the reversed recording medium to the toner image transfer position again; and a control section configured to, in the case of causing the conveyance section to convey the recording medium during double-sided printing, cause the transfer bias applying section to apply the transfer bias to the transfer roller while the recording medium passes through the toner image transfer position and then cause the transfer bias applying section to apply a reverse bias of the same polarity as the charge of the toner to the transfer roller during a period from the time when the recording medium has passed through the toner image transfer position to the time when the recording medium is conveyed again to the toner image transfer position after being reversed, characterized in that the control section is configured to perform, after the completion of the single-sided printing or the double-sided printing, a post-aging, by causing the transfer bias applying section to apply the reverse bias to the transfer roller, and, to calculate an execution time for the post-aging so that the ratio of a total time of application of the reverse bias performed by the image forming apparatus to a total time of application of the transfer bias performed by the image forming apparatus is a predetermined ratio.