This invention provides a clock switching circuit that can switch clocks without causing a hazard or a distortion of a duty ratio of the clocks. The clock switching circuit of this invention includes a first synchronization circuit that synchronizes a clock selection signal with a first clock, a second synchronization circuit that synchronizes with a second clock the clock selection signal that has been synchronized with the first clock by the first synchronization circuit and a clock selection circuit that outputs “1”, that is a high level, in synchronization with the clock selection signal that has been synchronized with the first clock by the first synchronization circuit and after that selects the second clock in synchronization with the clock selection signal that has been synchronized with the second clock by the second synchronization circuit.