Time measuring circuitry has a ring oscillator, a time-to-digital converter, a time measurer and a phase randomizer. The ring oscillator has a plurality of delay circuitries connected in a ring shape, the ring oscillator adjusting delay times of the plurality of delay circuitries based on an oscillation control signal to generate an oscillation signal. The time-to-digital converter quantizes a phase of the oscillation signal at a transition timing of a reference signal. The phase synchronizing circuitry to generate the oscillation control signal based on an output signal of the time-to-digital converter so that a phase of the oscillation signal coincides with a phase of the reference signal. The time measurer to measure a time interval based on the output signal of the time-to-digital converter. The phase randomizer to randomly shift the phase of the oscillation signal to be locked by the phase synchronizing circuitry.