5. A speech correction apparatus according to claim 1 , wherein the signal separating unit comprises: a filter having an acoustic characteristic as an impulse response of an acoustic system between the speaker and the microphone; and an operating unit for subtracting a signal which is obtained by passing a signal supplied to the speaker according to the speech to be corrected through the filter from a signal received from the microphone when the speech to be corrected is generated by the speaker, wherein a signal corresponding to the speech to be corrected is supplied by the filter and a signal corresponding to the ambient noise is supplied from the operating unit, so that the ambient noise is separated from the speech to be corrected at the hearing position; the speech correction apparatus further comprising: a coefficient update unit for updating a filter coefficient of the filter so that the power of the signal supplied from the operating unit is minimized; and a filter initial setting unit for setting an initial value of the filter coefficient, which is updated by the coefficient update unit, at a value other than 0.
8. A speech correction apparatus according to claim 5 , wherein the initial value set by the filter initial setting unit is a filter coefficient which corresponds to the model of a car carrying the apparatus.