An electroencephalogram measuring apparatus and method. The electroencephalogram measuring method includes detecting electroencephalogram data of an experimentee, amplifying the detected electroencephalogram data, and converting the data into a digital signal. Also, provided is a high-speed Fourier transforming the converted digital electroencephalogram data, calculating an output value for each frequency of the Fourier transformed electroencephalogram, calculating an output value for each frequency of the electroencephalogram for a predetermined time interval and calculating a relative output value for the ground state of the experimentee. Further provided is comparing the calculated relative output value for each frequency for each predetermined time interval for the ground state of the experimentee, with a predetermined value.