A biological state estimation device configured to estimate a biological state of a person by using a biosignal, the biological state estimation device comprising a biological state estimation means configured to estimate the biological state by using a pseudo heart sound waveform corresponding to a period of heart sound, and obtaining the pseudo heart sound waveform by processing biological sound and vibration information which is collected as the biosignal from a back of the person and fluctuates according to a flow rate of blood pumped out from the heart, characterized in that the biological state estimation means is furthermore configured to plot amplitudes (i, i+1) of adjacent two waveform components in one cardiac cycle of the pseudo heart sound waveform in a time-series manner in a coordinate system, with one of the amplitudes taken on the axis of abscissas and the other taken on the axis of ordinates, and to estimate the biological state from a variance state of a group of the plotted points, and the biological state estimation means is configured to estimate the biological state from a gradient of an approximate line of the group of the plotted points by comparing the gradient angle of the approximate line of the group of the plotted points with a correlation data of a blood pressure and the gradient angle of the approximate line which is stored in a storage in advance, wherein the biological state estimation includes a blood pressure fluctuation estimation which estimates a state of blood pressure fluctuation as the biological state, and wherein the pseudo heart sound waveform is a second pseudo heart sound waveform, Pseudo-PCG, including pseudo first and second sounds, the second pseudo heart sound waveform is obtained by: filtering an original waveform, RC0, of the back sound and vibration information by a band pass filter with a center frequency of around 20 Hz to obtain a first pseudo heart sound waveform, RC1; giving a distortion to the first pseudo heart sound waveform, RC1, by a clipping processing, wherein a threshold of the amplitude at the time of the clipping processing is set at such a position that a time width corresponding to that between first and second heart sounds in a heart sound waveform can be secured, to obtain a clipped waveform, Clip; and applying a high pass filter to the clipped waveform, Clip, to exclude signals except those at clipped parts and emphasize the pseudo first and second sounds. a biological state estimation means configured to estimate the biological state by using a pseudo heart sound waveform corresponding to a period of heart sound, and obtaining the pseudo heart sound waveform by processing biological sound and vibration information which is collected as the biosignal from a back of the person and fluctuates according to a flow rate of blood pumped out from the heart, characterized in that the biological state estimation means is furthermore configured to plot amplitudes (i, i+1) of adjacent two waveform components in one cardiac cycle of the pseudo heart sound waveform in a time-series manner in a coordinate system, with one of the amplitudes taken on the axis of abscissas and the other taken on the axis of ordinates, and to estimate the biological state from a variance state of a group of the plotted points, and the biological state estimation means is configured to estimate the biological state from a gradient of an approximate line of the group of the plotted points by comparing the gradient angle of the approximate line of the group of the plotted points with a correlation data of a blood pressure and the gradient angle of the approximate line which is stored in a storage in advance, wherein the biological state estimation includes a blood pressure fluctuation estimation which estimates a state of blood pressure fluctuation as the biological state, and wherein the pseudo heart sound waveform is a second pseudo heart sound waveform, Pseudo-PCG, including pseudo first and second sounds, the second pseudo heart sound waveform is obtained by: filtering an original waveform, RC0, of the back sound and vibration information by a band pass filter with a center frequency of around 20 Hz to obtain a first pseudo heart sound waveform, RC1; giving a distortion to the first pseudo heart sound waveform, RC1, by a clipping processing, wherein a threshold of the amplitude at the time of the clipping processing is set at such a position that a time width corresponding to that between first and second heart sounds in a heart sound waveform can be secured, to obtain a clipped waveform, Clip; and applying a high pass filter to the clipped waveform, Clip, to exclude signals except those at clipped parts and emphasize the pseudo first and second sounds. filtering an original waveform, RC0, of the back sound and vibration information by a band pass filter with a center frequency of around 20 Hz to obtain a first pseudo heart sound waveform, RC1; giving a distortion to the first pseudo heart sound waveform, RC1, by a clipping processing, wherein a threshold of the amplitude at the time of the clipping processing is set at such a position that a time width corresponding to that between first and second heart sounds in a heart sound waveform can be secured, to obtain a clipped waveform, Clip; and applying a high pass filter to the clipped waveform, Clip, to exclude signals except those at clipped parts and emphasize the pseudo first and second sounds.