A communication terminal device includes: an application acquisition section that acquires an application prepared to operate an image forming apparatus; an instruction acceptance section that accepts an operation instruction for processing indicated by the application; a processing executing section that makes the application runnable under an operating system of the communication terminal device and executes, in accordance with the application, the processing indicated by the operation instruction accepted by the instruction acceptance section; and a communication section that sends to the image forming apparatus a result of the processing executed by the processing executing section and an operation request.