An image processing device acquires a selection instruction to select one of a plurality of functions; and determines whether an operation mode is in a simulation mode in which a specific function is executed according to an instruction from a terminal device, which stores a virtual application program and a virtual service program used for the virtual application program. The device executing, in a case of determining that the operation mode is not the simulation mode, a first function executing process to execute the selected function by: activating the application program corresponding to the selected function, and executing, in a case of determining that the operation mode is the simulation mode, a second function executing process to execute the specific function by: inhibiting activation of the application program; publishing an API corresponding to the specific function; and acquiring an instruction for executing the specific function from the virtual application program.