Abstract: An information processing device connected to a terminal device of a subject and which visualizes emotion of the subject includes a data managing section that acquires at least data related to voice, a facial expression image, and a pulse wave of the subject; an emotion expression engine section which calculates a brain fatigue level based on a frequency of the voice, which calculates a mood level by extracting an emotion of the subject from the facial expression image, and which calculates a stress level by performing a frequency analysis of the pulse wave by fast Fourier transform and extracting a high-frequency section and a low-frequency section; and a three-axes processing section which displays a graph of points plotted at coordinates corresponding to the brain fatigue level, the mood level, and the stress level in a three-dimensional space defined by an X-axis, a Y-axis, and a Z-axis.