Abstract: An electronic tuner for musical instruments is disclosed which has built therein a voltage-controlled reference oscillator having its oscillation frequency controlled by a control signal and in which the oscillation signal of the reference oscillator and an input musical sound signal from a microphone are phase compared by a phase comparator and the oscillator is controlled by the phase compared output so that its oscillation frequency is synchronized with the frequency of the input musical sound signal. A control voltage, which is obtained when the oscillation frequency of the reference oscillator is synchronized with the frequency of the input musical sound signal, is applied to an indicator to indicate the ratio between the two frequencies.