An image forming apparatus including a plurality of operation modes, comprising: an image reading section configured to read image information from a document; an image recording section configured to record the image information on a medium selectively in a first operation mode where the image recording section operates at a first speed and in a second operation mode where the image recording section operates at a second speed lower than the first speed, the image forming apparatus requiring first power consumption when the image recording section operates in the first operation mode and second power consumption smaller than the first power consumption when the image recording section operates in the second operation mode; an electric power supply configured to supply electric power to the image reading section and the image recording section; a controller (71, 80) that controls the image recording section; a computing section configured to compute forecast power consumption (Wa) supplied to the image forming apparatus from the electric power supply when the image forming apparatus operates in a given one or more of the plurality of operation modes; and a determining section configured to determine whether the forecast power consumption (Wa) exceeds a reference value (Wmax); characterised in that when the image recording section is operating in the first operation mode, if the image forming apparatus receives an operation command for a third operation mode, the computing section adds power consumption required for the third operation mode to the first power consumption to obtain the forecast power consumption (Wa), and if the determining section determines that the obtained forecast power consumption (Wa) exceeds the reference value (Wmax), the controller (71, 80) drives the image recording section to halt the operation in the first operation mode, and then shifts the image recording section from the first operation mode to the second operation mode, and the image forming apparatus performs the second operation mode and the third operation mode so that at least a part of the third operation mode is performed concurrently with the second operation mode. an image reading section configured to read image information from a document; an image recording section configured to record the image information on a medium selectively in a first operation mode where the image recording section operates at a first speed and in a second operation mode where the image recording section operates at a second speed lower than the first speed, the image forming apparatus requiring first power consumption when the image recording section operates in the first operation mode and second power consumption smaller than the first power consumption when the image recording section operates in the second operation mode; an electric power supply configured to supply electric power to the image reading section and the image recording section; a controller (71, 80) that controls the image recording section; a computing section configured to compute forecast power consumption (Wa) supplied to the image forming apparatus from the electric power supply when the image forming apparatus operates in a given one or more of the plurality of operation modes; and a determining section configured to determine whether the forecast power consumption (Wa) exceeds a reference value (Wmax); characterised in that when the image recording section is operating in the first operation mode, if the image forming apparatus receives an operation command for a third operation mode, the computing section adds power consumption required for the third operation mode to the first power consumption to obtain the forecast power consumption (Wa), and if the determining section determines that the obtained forecast power consumption (Wa) exceeds the reference value (Wmax), the controller (71, 80) drives the image recording section to halt the operation in the first operation mode, and then shifts the image recording section from the first operation mode to the second operation mode, and the image forming apparatus performs the second operation mode and the third operation mode so that at least a part of the third operation mode is performed concurrently with the second operation mode.