a data processing apparatus has a first processing unit for processing an input data , a second processing unit responsive to the data processed by the first processing unit for executing a processing dependent on the data and producing a display data , and a display unit having a display drive unit and a display device for displaying the display data . the second processing unit is selectively inactivated and activated under control of the first processing unit to reduce power consumption in the second processing unit . the display drive unit is also selectively inactivated and activated under control of the first processing unit to reduce power consumption in the display unit . the display device has a memory function that maintains its display image even when supply of a display drive signal from the display drive unit is stopped , so that a latest image before inactivation of the second processing unit and / or the display drive unit for power consumption reduction is visible by an operator during the inactivated and low power consumption state of the apparatus .