To enable a controller to calculate the width of a phase shift accompanying variation in clock width and adjust the phase shift width while monitoring it by a comparator by finding the phase difference value based upon the variation in clock width and automatically adjusting a current phase difference value to it.

The data processor is equipped with a 1st flip-flop 11 which is controlled with a 1st clock A having pulse width X and a 2nd flip-flop 12 which is controlled with a 2nd clock B having the same pulse width X and a phase difference Y from the 1st clock A. Then, this data transfer method varies the pulse width X of and the phase difference Y between the 1st and 2nd clock pulses by variation quantities of the same rate for data transfer between the 1st and 2nd flip-flops.