A method of monitoring a blood pressure includes: emitting a laser to a blood vessel in a body part; detecting, from the body part, laser speckles caused by scattering of the emitted laser; obtaining a bio-signal indicating a change in a volume of the blood vessel by using the detected laser speckles; and estimating a blood pressure based on the obtained bio-signal. The plurality of contacts are placed so that their contact parts are in two rows along opposing inner wall surfaces of an insertion concavity of the housing. The health care practice management system also provides a vehicle to message targeted groups of individuals, namely, practitioners, patients, and miners of the practice data. Therefore the lens can be easily changed, but not prone to come off inadvertently. The branch pipe defines a hand hole for use in inspecting the circuit breaker, provides a place for installing an absorbent container and forms a foreign matter collecting space.