An analog-to-digital converter may include an annular delay circuit that includes a plurality of delay units connected in an annular shape, each of the plurality of delay units delaying a pulse current that is input to each of the plurality of delay units, a current source that outputs an electric current, in accordance with an input analog signal, to selected delay units, which is selected from among the plurality of delay units, and a digital signal generation unit that generates a digital signal in accordance with a number of circulations per predetermined period of time of the pulse current circulating around the annular delay circuit.