A biological data observation apparatus includes a measuring unit including at least a photoelectric sensor including a light emitting element for emitting light with a predetermined wavelength onto a blood vessel of a subject and a light detecting element for detecting, as a photoelectric volume pulse wave, a change in an amount of transmitted or reflected light resulting from the light emitted from the light emitting section, a storage area in which pressure conversion data correlating a pulse wave area and a blood pressure value in order that the pulse wave area may be converted to the blood pressure value as an absolute value, the pulse wave area being obtained by integrating a wave form of the photoelectric capacity pulse wave per heartbeat, an operational unit calculating the pulse wave area on the basis of the photoelectric volume pulse wave obtained from the subject and further calculating the blood pressure value of the subject on the basis of the calculated pulse wave area and the blood pressure conversion data, and a display unit displaying a result of calculation performed by the operational unit.