This invention provides a signal processing apparatus for improving the speech determination accuracy in an input sound. The signal processing apparatus includes a transformer that transforms an input signal into an amplitude component signal in a frequency domain, a calculator that calculates a norm of a change in the amplitude component signal in a frequency direction, an accumulator that accumulates the norm of the change in the amplitude component signal in the frequency direction calculated by the calculator, and an analyzer that analyzes speech in the input signal in accordance with an accumulated value of the norm of the change in the amplitude component signal in the frequency direction calculated by the accumulator.