An electronic keyboard musical instrument includes a sound source configured to, in response to detection of key-pressing of the first key in damper-off detection, input first excitation signal data corresponding to the first key to a first channel, input first channel output data which is output from the first channel to each of low-register channels corresponding to the respective low-register keys, and output musical sound data which is generated based on respective pieces of low-register channel output data which is output from the respective low-register channels and the first channel output data, as musical sound data corresponding to the first key.