Flows of data are controlled using an externally supplied clock. A clock-synchronized C-element C1 outputs a sending signal S1 of H level to a data latch DL1 and the subsequent clock-synchronized C-element C2 and outputs an acknowledge signal A1 of H level, in synchronization with a rise of a clock signal CLK1 which is inputted to the clock-synchronized C-element C1 after the clock-synchronized C-element C1 receives a sending signal S0 of H level. Following this, the clock-synchronized C-element C1 causes the acknowledge signal A1 to fall by the next rise of the clock signal CLK1. This latches the data latch DL1. A clock signal CLK2 rises before the clock signal CLK1 falls and rises once again. In synchronization with this rise, the clock-synchronized C-element C2 performs a similar operation. As a result, the precedent clock-synchronized C-element C1 causes the sending signal S1 to fall.