PURPOSE: To easily monitor the blood component particularly during sleep by providing a light emitting element which irradiates the inside of the tissue of a living body with light and a light receiving element which receives the light and outputs the light reception signal corresponding to the blood component in the tissue, and transmitting vibration energy in accordance with the light reception signal.

CONSTITUTION: This portable device has the light emitting element 2 which emits the light toward the inside of the tissue, the light receiving element 3 which receives the light past the inside of the tissue from the light emitting element 2 and a blood monitor card 1 which contains a battery 4. This card 1 is mounted on the clothing of a patient in correspondence to the surface of the patient's skin of the part where the blood pressure is to be measured. The current signal from the light receiving element 3 is arithmetically processed by a light emitting/light receiving D/A converter 5 within this monitor card 1 and the value corresponding to the concn. of the in-blood component, for example, oxygen, in the tissue, is outputted. This computed value is stored in a storage circuit the output side of the storage 7 and the computed value is transmitted as the vibration energy 9, such as high-frequency magnetic field or ultrasonic wave, from a wave transmitter 10.