An image forming apparatus comprising: a print unit which includes a container containing a colorant and which is configured to perform a printing operation on one side of a sheet conveyed along a printing conveyance path; an inversion mechanism configured to receive the sheet from the print unit and sent the sheet via an inversion conveyance path back to the print unit with the front and rear surfaces of the sheet inverted; a control unit configured to control the print unit and the inversion mechanism to perform a double-side printing operation method, wherein first an operation of printing images on one side of N non-printed sheets (N ≥ 1), respectively, is performed by the print unit to obtain N one-side printed sheets, and then thereafter an operation of printing images on the opposite side of M of the N one-side printed sheets, which are fed to the print unit with the front and rear surfaces of the sheet inverted by the inversion mechanism, using the colorant is performed by the print unit before another operation of printing on one side of a non-printed sheet by the print unit is performed; and a determination unit which is configured to determine whether an amount of the colorant remaining in the container is equal to or greater than a threshold value, wherein the control unit is configured to control the print unit to perform a normal printing operation and a reduced printing operation using an amount of colorant smaller than that of the normal printing operation, and wherein the control unit is configured to control the print unit to perform the reduced printing operation with the reduced amount of colorant when the determination unit determines that the amount of the remaining colorant is less than the threshold value, characterized in that the control unit is configured to control the print unit to perform the reduced printing operation on one side of a new non-printed sheet but to perform the normal printing operation instead of the reduced printing operation on the opposite side of a one-side printed sheet already existing at the time that the determination unit determines that the amount of the remaining colorant is less than the threshold value. a print unit which includes a container containing a colorant and which is configured to perform a printing operation on one side of a sheet conveyed along a printing conveyance path; an inversion mechanism configured to receive the sheet from the print unit and sent the sheet via an inversion conveyance path back to the print unit with the front and rear surfaces of the sheet inverted; a control unit configured to control the print unit and the inversion mechanism to perform a double-side printing operation method, wherein first an operation of printing images on one side of N non-printed sheets (N ≥ 1), respectively, is performed by the print unit to obtain N one-side printed sheets, and then thereafter an operation of printing images on the opposite side of M of the N one-side printed sheets, which are fed to the print unit with the front and rear surfaces of the sheet inverted by the inversion mechanism, using the colorant is performed by the print unit before another operation of printing on one side of a non-printed sheet by the print unit is performed; and a determination unit which is configured to determine whether an amount of the colorant remaining in the container is equal to or greater than a threshold value, wherein the control unit is configured to control the print unit to perform a normal printing operation and a reduced printing operation using an amount of colorant smaller than that of the normal printing operation, and wherein the control unit is configured to control the print unit to perform the reduced printing operation with the reduced amount of colorant when the determination unit determines that the amount of the remaining colorant is less than the threshold value, characterized in that the control unit is configured to control the print unit to perform the reduced printing operation on one side of a new non-printed sheet but to perform the normal printing operation instead of the reduced printing operation on the opposite side of a one-side printed sheet already existing at the time that the determination unit determines that the amount of the remaining colorant is less than the threshold value.