Disclosed are a channel number variable type hearing aid and a method by which a hearing aid varies the number of channels. According to one aspect of the present embodiment, provided is the channel number variable type hearing aid comprising: a microphone for receiving an input of a sound signal; an AD converting unit for converting the sound signal input from the microphone into a digital signal and outputting same; a control unit for determining a filter bank channel for processing the digital signal output from the AD converting unit; a buffer unit for delaying the digital signal on the basis of the determined filter bank channel; a signal processing unit including at least one filter bank channel, synthesizing the digital signal by using the determined filter bank channel, and outputting same; a DA converting unit for converting the digital signal output from the signal processing unit into a sound signal and outputting same; and a speaker for outputting the sound signal output form the DA converting unit, wherein the control unit determines the filter bank channel for processing the digital signal, on the basis of a pre-set condition.