Frequency spreading circuit

A frequency spreading circuit comprising:

• a ring oscillator configured with a multiple number of logic inverting circuits in a ring shape for generating multi-phase clock signals;
• a period measuring unit configured to measure a period of a reference clock, which is inputted, by the multi-phase clock signals of the ring oscillator and output a measured period as a period data value;
• a frequency spreading calculation unit configured to calculate a frequency spreading command value in accordance with a frequency spreading rate, a frequency spreading period and the period data value of the period measuring unit, which are inputted;
• and
• a pulse generation unit configured to generate a clock pulse corresponding to the frequency spreading command value in accordance with a data value determined by addition of the frequency spreading command value to the period data value.