To provide a musical instrument, even if an internal space of a resonance section to which vibration of a vibrator is transmitted is small, issuing sound with a sound quality close to resonance characteristics when the internal space of the resonance section is large.

A guitar 1 includes: a trunk part 10 for resonating the vibration of a string 2 in an internal space; a microphone 30 converting a sonic wave reaching a boundary surface CA in the trank part 10, into an electric signal and outputting it; a signal processing part 100 performing, to the electric signal, a signal processing for providing sound effect according to the shape of a virtual resonance space that is virtually spread from the boundary surface CA outward the trunk part 10; and a speaker 40 converting the electric signal to which the signal processing is performed, into the sonic wave and outputting it from the boundary surface CA towards the internal space.