To provide a transmission suppression method and system in a dialup router that can automatically suppress transmission not intended by a user due to periodic communication or the like by an application program so as to prevent excess charging in the case of using an automatic channel access transmission of the dialup router.

When a LAN interface section 12 receives data addressed to a network 100, a control section 103 retrieves reception time information in a storage section 14 and reception interval information in a storage section 15 on the basis of a received time of a clock section 17, a sender IP address and a destination port number in the data and calculates and stores a data reception interval and number of counts denoting number of consecutive times of a prescribed data reception interval. Furthermore, when the LAN interface section 12 receives data from the same sender IP address addressed to the same destination port number for a predetermined number of times, the control section 13 invalidates data from the same sender IP address addressed to the same destination port number received at a prescribed reception interval after that.