Provided is a musical instrument controller capable of accurately controlling a musical sound parameter. This musical instrument controller includes: a reception means for receiving, from a musical performance device, a sound emission start signal transmitted on the basis of a musical performance operation; a sensor for detecting an amount of displacement from a reference position; and a control means for generating a control signal on the basis of the amount of displacement from the reference position and transmitting the control signal to a sound generation device. The control means sets the reference position on the basis of the sound emission start signal received from the musical performance device.