An image forming apparatus comprising: an image forming portion configured to form a toner image; a rotatable intermediary transfer belt onto which the toner image formed by said image forming portion is transferred; an inner roller contacting an inner peripheral surface of said intermediary transfer belt and configured to stretch said intermediary transfer belt; a transfer unit (41, 45, 46) contactable to an outer peripheral surface of said intermediary transfer belt and configured to form a transfer nip, where the toner image is transferred from said intermediary transfer belt onto a recording material, by nipping said intermediary transfer belt between itself and said inner roller, said transfer unit including an outer roller configured to form the transfer nip between said outer roller and said inner roller; a contact and separation mechanism configured to bring said transfer unit into contact with and separation from said intermediary transfer belt; a changing mechanism capable of changing a position of the transfer nip with respect to a circumferential direction of said inner roller by changing a position of said inner roller relative to the outer roller, wherein said changing mechanism is capable of changing the position of said inner roller to a first position where the position of the transfer nip corresponds to a first transfer position and to a second position where the position of the transfer nip corresponds to a second transfer position; a driving device configured to drive said intermediary transfer belt; and a controller configured to control said changing mechanism and said contact and separation mechanism, wherein in a case that said controller receives an instruction to start image formation when said outer roller is separated from said intermediary transfer belt, in a period after input of the instruction and before a transfer operation of the toner image on a first recording material, said controller controls said changing mechanism and said contact and separation mechanism so that: (i) movement of said inner roller is started so that the position of said inner roller is moved to a position corresponding to the position of the transfer nip set for transfer of the toner image on the first recording material, and then (ii) an operation of said contact and separation mechanism is started so that said transfer unit contacts said intermediary transfer belt. an image forming portion configured to form a toner image; a rotatable intermediary transfer belt onto which the toner image formed by said image forming portion is transferred; an inner roller contacting an inner peripheral surface of said intermediary transfer belt and configured to stretch said intermediary transfer belt; a transfer unit (41, 45, 46) contactable to an outer peripheral surface of said intermediary transfer belt and configured to form a transfer nip, where the toner image is transferred from said intermediary transfer belt onto a recording material, by nipping said intermediary transfer belt between itself and said inner roller, said transfer unit including an outer roller configured to form the transfer nip between said outer roller and said inner roller; a contact and separation mechanism configured to bring said transfer unit into contact with and separation from said intermediary transfer belt; a changing mechanism capable of changing a position of the transfer nip with respect to a circumferential direction of said inner roller by changing a position of said inner roller relative to the outer roller, wherein said changing mechanism is capable of changing the position of said inner roller to a first position where the position of the transfer nip corresponds to a first transfer position and to a second position where the position of the transfer nip corresponds to a second transfer position; a driving device configured to drive said intermediary transfer belt; and a controller configured to control said changing mechanism and said contact and separation mechanism, wherein in a case that said controller receives an instruction to start image formation when said outer roller is separated from said intermediary transfer belt, in a period after input of the instruction and before a transfer operation of the toner image on a first recording material, said controller controls said changing mechanism and said contact and separation mechanism so that: (i) movement of said inner roller is started so that the position of said inner roller is moved to a position corresponding to the position of the transfer nip set for transfer of the toner image on the first recording material, and then (ii) an operation of said contact and separation mechanism is started so that said transfer unit contacts said intermediary transfer belt. (i) movement of said inner roller is started so that the position of said inner roller is moved to a position corresponding to the position of the transfer nip set for transfer of the toner image on the first recording material, and then (ii) an operation of said contact and separation mechanism is started so that said transfer unit contacts said intermediary transfer belt.