A user authentication method using ultrasonic waves is disclosed. The user authentication method using ultrasonic waves, according to an embodiment of the present invention, comprises the steps of: receiving a sound wave signal which includes analog data; sampling the sound wave signal at a preset sampling rate; generating a block by selecting a preset number of pieces of sampling data; converting sampled data included in the block into frequency components; and determining, as digital data in the block, a letter or number corresponding to the frequency component having the largest magnitude from among the frequency components.