To provide a clock adjusting apparatus and a clock adjusting method of a high-speed serial bus which determines the best clocking point during an operation without stopping the operation and also obtains a clock margin.

A clock adjusting portion 100 has a best-point determining means to determine the best point among clock points in a high-speed serial data, a determining point setting means to set one or two or more from among the clocking points to the determining point for determining an effective range to receive the high-speed serial data correctly during the operation, a comparison means to compare input data of the best point with the input data of the deciding point, a point updating means to update the determining point based on the compared results, and a holding means to hold the effective range based on the updated determining point.