An image processing apparatus includes a noise reduction unit configured to nonlinearly convert a signal obtained by subtracting a value of a subtraction image signal, which is read from a memory, from that of a current-frame image signal, to generate a noise-reduced signal by subtracting the nonlinearly converted signal from the current-frame image signal, and to store the noise-reduced signal in the memory, a read unit configured to read the subtraction image signal from the memory at a moment between a moment, at which the subtraction image signal read from the memory is stored in the memory, and a moment at which the subtraction image signal is read from the memory, and a generation unit configured to generate an image based on the subtraction image signal read by the read unit.