An image forming apparatus comprising: image forming means adapted to form an image on a recording material; fixing means including a heat source configured to generate heat from electrical power, configured to fix the image formed on the recording material; and control means configured to control the operation of the fixing means, wherein, the image forming apparatus is operable to transfer from a stand-by mode to a power-saving mode, in which the electric power consumed by the image forming apparatus is smaller than the electric power consumed by the image forming apparatus in the stand-by mode, if the image forming apparatus does not receive a print job in the stand-by mode in a set time period, and the image forming apparatus further comprises: time period setting means (115, 118) configured to permit a user to set a time period for transferring to the power-saving mode, characterized in that the heat source is adapted to perform pre-heating of the fixing means in the stand-by mode, wherein the heat source is adapted not to perform pre-heating of the fixing means when the set time period is shorter than a reference time period such that the average electric power consumed in the stand-by mode is smaller than the average electric power consumed in the stand-by mode if the time period set by the user is longer than said reference period. image forming means adapted to form an image on a recording material; fixing means including a heat source configured to generate heat from electrical power, configured to fix the image formed on the recording material; and control means configured to control the operation of the fixing means, wherein, the image forming apparatus is operable to transfer from a stand-by mode to a power-saving mode, in which the electric power consumed by the image forming apparatus is smaller than the electric power consumed by the image forming apparatus in the stand-by mode, if the image forming apparatus does not receive a print job in the stand-by mode in a set time period, and the image forming apparatus further comprises: time period setting means (115, 118) configured to permit a user to set a time period for transferring to the power-saving mode, characterized in that the heat source is adapted to perform pre-heating of the fixing means in the stand-by mode, wherein the heat source is adapted not to perform pre-heating of the fixing means when the set time period is shorter than a reference time period such that the average electric power consumed in the stand-by mode is smaller than the average electric power consumed in the stand-by mode if the time period set by the user is longer than said reference period. time period setting means (115, 118) configured to permit a user to set a time period for transferring to the power-saving mode, characterized in that the heat source is adapted to perform pre-heating of the fixing means in the stand-by mode, wherein the heat source is adapted not to perform pre-heating of the fixing means when the set time period is shorter than a reference time period such that the average electric power consumed in the stand-by mode is smaller than the average electric power consumed in the stand-by mode if the time period set by the user is longer than said reference period.