A scan control method of a circuit device including setting information indicating scan mode in a register is provided. The scan control method includes cutting an output of scan-out data to a test access port controller and an input of scan-in data from a data register based on information set in the register, and controlling a connection between a scan register and a data register. Each data/scan register includes data registers for the same number of chains to be scanned at the same time. Data set in one data register may be kept in all the data registers in parallel and scanned in all the scan chains in a scan-in process in the broadcast mode. The data set in the data register may be kept in the data register corresponding to the scan register and scanned in the corresponding scan chain, in a scan-in process in the parallel mode.