Provided is a method of automatically fitting a hearing aid. The method includes the steps of entering an audiogram of a test subject, defining criterion gains and SSPLs according to the test subject's audiogram in each test frequency band, generating 70dB SPL long term speech spectrum noise, and measuring the gains and SSPLs of the amplified sound in front of test subject's eardrum using the probe tube microphone, comparing the measured gains and SSPLs with the criterion gains and SSPLs and if the measured gains and SSPLs are less than the criterion gains and SSPLs, increasing the gain and SSPL of the hearing aid and repeating measurement, and if the measured gains and SSPLs becomes equal to the criterion gains and SSPLs, setting the gains and SSPLs of the hearing aid at that time as an actual gain and/or SSPL of the hearing aid and saving the automatic fitting device.