A low-power and high-speed ADC includes: a successive approximation converter circuit configured to sequentially compare and coarsely convert the analog input signal voltage into a digital signal with a number of higher-order bits, and also to output a residual voltage; a fixed-quantity change time measurement converter circuit configured to finely convert the residual voltage into a digital signal with a number n of lower-order bits by changing the residual voltage at a fixed rate of change and by measuring the time until a predetermined value is reached; and an encoder circuit configured to generate a digital signal with the predetermined number of bits by combining the digital signal with the number of higher-order bits output from the successive approximation converter circuit and the digital signal with the number of lower-order bits output from the fixed-quantity change time measurement converter circuit.