The present invention provides a data processing apparatus which performs a data process via a LAN and a communication line other than the LAN comprises reception means for receiving data from a transmission side via the communication line notification means for notifying that the reception means received the data, to a plurality of receivers on the LAN transmission means for transmitting information representing a notification result by the notification means, to the transmission side timer means for performing a time count and control means for causing the transmission means to start the transmission, when it is judged by the timer means that a predetermined period of time is elapsed, so that it can be easily notified to the transmission side whether or not the data reception was notified to terminals on the LAN.