Among the technical characteristics disclosed in this specification, the pulse wave sensor with one of the technical characteristic includes a construction to detect the pulse wave at a wrist (i.e., a construction to measure the pulse wave to be worn at the wrist). To be more concrete, the pulse wave sensor includes a measurement unit to measure the pulse wave, a power source unit to supply power to the measurement unit, a cable to connect between the measurement unit and the power source unit electrically, and a armlet type housing to contain the measurement unit, the power source unit, and the cable.