A digital information restoring device is arranged to detect time between level transition points of a digital signal which indicates digital information by means of variations in its period, output the resultant period data, calculate an average value of at least two period data among the output period data, and compare the average value with the aforesaid period data, and restore the digital information. The digital information restoring device is, therefore, capable of restoring the digital information at a high speed without using a high-speed PLL circuit or the like. The digital information restoring device may also be arranged to perform time-axis expansion of only part of the received period data, and input the resultant period data to a computing circuit to restore the digital information.