Electronic musical instrument of delayed feedback type

In a tone signal synthesizer for synthesizing a tone signal by supplying a driving signal, into a closed loop circuit including a delay circuit and a filter, a filter coefficient which controls the characteristic of the filter is changed while a musical tone is generated. For example, a set of filter coefficients are provided at the time of key-on and are switched to another set of filter coefficients when a predetermined time is passed after the time of key-on. The set of filter coefficients are switched to a further set of filter coefficients at the time of key-off and then are switched to a still further set of filter coefficients when a predetermined time is passed after the time of key-off. It is possible to generate a musical tone which changes more complexly on the basis of the change of the filter characteristic, with the passage of time.