A novel technique for analyzing a biological state is provided. A body trunk biological signal (aortic pulse wave) extracted from the back of a body trunk is differentiated twice. By using a resultant second derivative waveform, a waveform component of a maximum amplitude of a low frequency appearing as a result of switch of an amplitude from attenuation to amplification in transition from a contracting phase to a diastolic phase of a ventricle is specified in each period of the second derivative waveform. Inflection points are specified that appear before and after the maximum amplitude waveform component. A biological state is analyzed using information about each of the inflection points. The two inflection points obtained from a reference form of the second derivative waveform of the aortic pulse wave substantially agree in time phase with first heart sound and second heart sound (or an R wave and a T wave in an electrocardiogram) indicating the dynamic state of a cardiovascular system. This enables analysis of a biological state.