A person who is elderly, requires care, or an inpatient who is under the
care by his or her family members, a nursing care worker, or a nurse in a
hospital or medical institution must be monitored constantly, however the
caregiver cannot be in attendance on the patient all the time. A
biosignal intensity measuring method is provided to solve the above
problem. According to the measuring method, output signals from a
noninvasive sensor, which detects biosignals from a lying subject, are
amplified and noises other than the biosignals are attenuated via a
signal amplifying/shaping unit, and the amplified signals are controlled
by an automatic gain control (AGC) unit to have sizes within a prescribed
range, then parameters acquired by signal gains in a control circuit upon
carrying out automatic gain control are output as the output signal
intensity of the biosignals to calculate biosignal intensity. A bedding
state monitoring method is also provided. According to the monitoring
method, the calculated signal intensity is used to monitor the bedding
state of the subject, such as a state of being in or out of bed, of
weakening or stoppage of biosignals, of body motion, or the like.