Abstract: A biological state monitoring system (100) for monitoring a biological state of a subject on a bed (BD) over a predetermined monitoring period, includes: at least one load detector (11, 12, 13, 14) configured to detect a load of the subject on the bed; and a respiratory rate estimating unit (34) configured to successively obtain and output estimated values of a respiratory rate of the subject, based on a temporal variation of a detection value of the load detector. The monitoring period includes a body motion period in which the subject has a body motion, and a resting period in which the subject merely performs a respiration.