A sound processing apparatus which is arranged to process a first sound signal and a second sound signal, the sound processing apparatus comprising: a signal input unit to supply a sound signal; a first filter to selectively pass a band component of the sound signal corresponding to a reproduction band of a first speaker in which a lower limit value of the reproduction band is set to be a first frequency as a first sound signal and a second filter (62R, L) to selectively pass a band component of the sound signal corresponding to a reproduction band of a second speaker in which a lower limit value of the reproduction band is set to be a second frequency beyond the first frequency as a second sound signal; a first adjustor which is arranged to adjust a volume of the first sound signal; a second adjustor which is arranged to adjust a volume of the second sound signal; and a control unit which is arranged to cause the first adjustor and the second adjustor to adjust the first sound signal so that it is gradually changing over a first gradual-change time period and the second sound signal so that it is gradually changing over a second gradual-change time period to perform a transition from a normal reproduction state to a silence state or to perform a transition from a silence state to a normal reproduction state, wherein the second gradual-change time period is shorter than and included in the first gradual-change time period, wherein the control unit is arranged to control the first adjustor and the second adjustor to cause fade-out of the first sound signal and fade-out of the second sound signal or fade-in of the first sound signal and fade-in of the second sound signal to start or end at a common point in time. a signal input unit to supply a sound signal; a first filter to selectively pass a band component of the sound signal corresponding to a reproduction band of a first speaker in which a lower limit value of the reproduction band is set to be a first frequency as a first sound signal and a second filter (62R, L) to selectively pass a band component of the sound signal corresponding to a reproduction band of a second speaker in which a lower limit value of the reproduction band is set to be a second frequency beyond the first frequency as a second sound signal; a first adjustor which is arranged to adjust a volume of the first sound signal; a second adjustor which is arranged to adjust a volume of the second sound signal; and a control unit which is arranged to cause the first adjustor and the second adjustor to adjust the first sound signal so that it is gradually changing over a first gradual-change time period and the second sound signal so that it is gradually changing over a second gradual-change time period to perform a transition from a normal reproduction state to a silence state or to perform a transition from a silence state to a normal reproduction state, wherein the second gradual-change time period is shorter than and included in the first gradual-change time period, wherein the control unit is arranged to control the first adjustor and the second adjustor to cause fade-out of the first sound signal and fade-out of the second sound signal or fade-in of the first sound signal and fade-in of the second sound signal to start or end at a common point in time.