An apparatus comprising: a washing machine, a drying machine disposed on the washing machine, and a control panel. The control panel including a first user interface configured to control the washing machine, a second user interface configured to control the drying machine, a first start/pause button configured to receive an input for starting or pausing an operating of the washing machine, a second user interface configured to receive an input for controlling the drying machine, and a display configured to display operation information of the washing machine and operation information of the drying machine. The apparatus configured to control an operation of the drying machine in response to an input received through the second start/pause button while operation information of the washing machine is displayed on the display.