A circuit startup method utilizing utterance estimation in a speech processing system including a sound collecting device is provided. The circuit startup method includes a subset power supply step of supplying power to the sound collecting device and a signal processing circuit, and a sound collecting step of inputting a sound from the sound collecting device through the signal processing circuit. The circuit startup method further includes an utterance estimation step of estimating whether or not a speech is contained in the inputted sound, and a power supply step of supplying power to the speech processing circuit for an utterance interval when it is estimated that a speech is contained from an estimation result of the utterance estimation step.