A method of controlling an image forming operation conducted in an image forming apparatus, the image forming apparatus comprising: a plurality of image bearing members (11a - 11d); a rotatable intermediary transfer member for carrying toner images transferred from said plurality of image bearing members (11a - 11d) in contact with said plurality of image bearing members (11a - 11d); a transfer member for press-contacting to said intermediary transfer member to form a transfer portion, at which the toner images on said intermediary transfer member are to be transferred onto a recording material; and a control portion for conducting the controlling of the image forming operation, wherein the controlling of the image forming operation comprises: executing a continuous image forming mode in which images are formed on a plurality of recording materials, selecting a preset minimum interval with which the plurality of recording materials is conveyed during the continuous image forming mode, wherein in the image forming operation a recording material passes through the transfer portion and thereafter transfer of a toner image to be formed on a subsequent recording material from a last image bearing member which is located upstream of the transfer portion and most downstream of said plurality of image bearing members (11a - 11d) with respect to a rotational direction of said intermediary transfer member, onto said intermediary transfer member is started, wherein transfer of a toner image to be formed on a subsequent recording material from the image bearing members (11a - 11c) being different to the last image bearing member is started before the recording material passes through the transfer portion. a plurality of image bearing members (11a - 11d); a rotatable intermediary transfer member for carrying toner images transferred from said plurality of image bearing members (11a - 11d) in contact with said plurality of image bearing members (11a - 11d); a transfer member for press-contacting to said intermediary transfer member to form a transfer portion, at which the toner images on said intermediary transfer member are to be transferred onto a recording material; and a control portion for conducting the controlling of the image forming operation, wherein the controlling of the image forming operation comprises: executing a continuous image forming mode in which images are formed on a plurality of recording materials, selecting a preset minimum interval with which the plurality of recording materials is conveyed during the continuous image forming mode, wherein in the image forming operation a recording material passes through the transfer portion and thereafter transfer of a toner image to be formed on a subsequent recording material from a last image bearing member which is located upstream of the transfer portion and most downstream of said plurality of image bearing members (11a - 11d) with respect to a rotational direction of said intermediary transfer member, onto said intermediary transfer member is started, wherein transfer of a toner image to be formed on a subsequent recording material from the image bearing members (11a - 11c) being different to the last image bearing member is started before the recording material passes through the transfer portion. executing a continuous image forming mode in which images are formed on a plurality of recording materials, selecting a preset minimum interval with which the plurality of recording materials is conveyed during the continuous image forming mode, wherein in the image forming operation a recording material passes through the transfer portion and thereafter transfer of a toner image to be formed on a subsequent recording material from a last image bearing member which is located upstream of the transfer portion and most downstream of said plurality of image bearing members (11a - 11d) with respect to a rotational direction of said intermediary transfer member, onto said intermediary transfer member is started, wherein transfer of a toner image to be formed on a subsequent recording material from the image bearing members (11a - 11c) being different to the last image bearing member is started before the recording material passes through the transfer portion.