The present invention is a method for adjusting power consumption in a network system including a first communication device and a second communication device communicating with the first communication device, wherein the method includes the first communication device creating IC operation information related to the operation of a first information processing IC in the first communication device and sending the IC operation information to the second communication device; the second communication device acknowledging the sent IC operation information in whole or in part and sending the acknowledged IC operation information to the first communication device; and the first communication device adjusting the driving frequency and/or the supply voltage of the first information processing IC according to the acknowledged IC operation information.