In an interface control semiconductor integrated circuit including a plurality of protocol circuits for processing a protocol such as AV- or PC-oriented protocols engaged in an IEEE 1394 standard-compliant data transmission, power consumption is reduced. To achieve this, the interface control semiconductor integrated circuit including the protocol circuits is provided with a plurality of switches associated with the respective protocol circuits and each of the switches performs a switching between supply and shut-off of a clock. A clock is supplied to one of the protocol circuits which should be used whereas clock to unused protocol circuits are shut-off, by controlling each of the switches.