A data processing apparatus includes: a receiving unit configured to receive input data including processing-target data from outside; a measuring unit configured to measure the data amount of the processing-target data included in the received input data; a data processing unit configured to perform predetermined processing on the processing-target data, and to output a result of the processing as output data; and a control unit configured to set the data processing unit to an active state based on reception of the input data by the receiving unit, and when the data amount of the output data reaches the data amount of data obtained by performing the predetermined processing on data of the data amount measured by the measuring unit, to set the data processing unit to a sleep state.