A data processing apparatus includes an input unit to read out data of a first area of image data from an external memory, sequentially interpret commands included in a command list, and transmit the data of the first area to an image processing unit according to the command, and an output unit to receive data obtained by performing a image processing on the data of the first area and write the received data in the external memory, whereon, based on a control signal, the input unit controls readout of a following command to a command indicating suspension from the external memory and continuation, etc., of transmission of the data of a second area, and based on a control signal, the output unit controls, in a case that the command indicating suspension is received, continuation, etc., of writing of the data of the second area to the external memory.