Abstract: A serial bus controller comprises a competition result discriminator for outputting a lost competition signal DB upon detecting a lost competition, by comparing a clock SCK and data SDA on a serial communication bus against a clock CKO and data DAO, respectively, to be output from the own station to find any difference between them, a bus release controller for performing end-of-communication procedures including releasing the serial communication bus in response to the lost competition signal DB, and a slave mode setting section for effecting slave mode setting procedures in response to the lost competition signal DB and based on the data SDA on the serial communication bus.