An analog-to-digital converter (1) includes an S/H circuit (10) configured to sample and hold an analog input signal (IN) in synchronization with a sampling clock signal (CLK), a delay circuit (20) configured to delay the sampling clock signal (CLK), an ADC circuit (30) configured to sample an output signal (S/H_out) of the S/H circuit (10) in synchronization with the sampling clock signal (CLK_delay) that is delayed, and output a digital signal (OUT) corresponding to an amplitude of the output signal that is sampled, and a delay adjustment circuit (40) configured to adjust a delay time of the sampling clock signal (CLK) in the delay circuit (20) in accordance with a change in frequency of the sampling clock signal (CLK).