Hearing aid with variable number of channels and method of switching number of channels of hearing aid

A hearing aid with the variable number of channels includes: a microphone that receives a sound signal; an AD converter that converts the sound signal input from the microphone into a digital signal and outputs the converted digital signal; a controller that determines a filter bank channel for processing the digital signal output from the AD converter; a buffer unit that delays the digital signal based on the determined filter bank channel; a signal processor that includes at least one filter bank channel, synthesizes the digital signal using the determined filter bank channel and outputs the synthesized digital signal; a DA converter that converts the digital signal into the sound signal and outputs the converted sound signal; and a speaker that outputs the sound signal output from the DA converter, in which the controller determines the filter bank channel for processing the digital signal based on a preset condition.