A sleep state monitoring system is provided a pressure sensor, an optical sensor, and a controller. The pressure sensor detects a change in pressure of a pulse wave propagating through a blood vessel to measure a voltage value as a first voltage value of arterial pressure, and the optical sensor detects a change in pressure of a pulse wave propagating through the blood vessel by use of an optical signal to measure a voltage value as a second voltage value of a vascular pulse wave signal. The controller determines a sleep state of the human body, based on the first voltage value and the second voltage value.
