Image forming apparatus with two-sided copying and variable image data transfer clock frequency

An image forming apparatus, comprising:

• a tray on which an original bundle is stacked;
• a feeding unit configured to feed an original from the tray one by one to a conveyance path;
• a first reading unit configured to read an image of a first surface of the original conveyed through the conveyance path;
• a second reading unit, provided downstream of the first reading unit in the conveyance path, configured to read an image of a second surface of the original;
• a first storage unit configured to temporarily store image data generated by the first reading unit and the second reading unit;
• a clock generator configured to generate a transfer clock;
• a transmitter configured to transfer the image data stored in the first storage unit based on the transfer clock;
• a second storage unit configured to store the image data transferred by the transmitter;
• and
• an image forming unit configured to form an image based on the image data stored in the second storage unit,
• wherein in a case where copying of the original bundle is executed, a frequency of a first transfer clock for transferring image data of the first surface of a first original in the original bundle is lower than a frequency of a second transfer clock for transferring image data of the second surface of the first original and image data of the first surface of a second original in the original bundle.