A biosensor device comprising: at least one pair of electrocardiographic electrodes (19, 24) for detecting electrical signals of a living body, insulating films (20, 25) disposed on the at least one pair of electrocardiographic electrodes (19, 24) and having one surfaces, which are positioned oppositely away from the other surfaces being in contiguity with the at least one pair of electrocardiographic electrodes (19, 24) and which serve as contact surfaces to be contacted with the living body, a light emitter (8,9) for emitting light to the living body, a light receiver for receiving the light emitted from the light emitter after being reflected by the living body, and a processing circuit (26, 52, 62) including an electrocardiographic signal detection unit (27, 53, 63) for generating an electrocardiographic signal by differentially amplifying the electrical signals of the living body, which are detected through capacitive coupling between the living body contacted with the contact surfaces of the insulating films (20, 25) and the at least one pair of electrocardiographic electrodes (19, 24), and a photo-plethysmographic signal detection unit for generating a photo-plethysmographic signal based on the light emitted from the light emitter (8,9) and the light received by the light receiver, characterised in that: at least one of the at least one pair of electrocardiographic electrodes (19,24) is a light transmissive electrocardiographic electrode (19, 43) made of an electroconductive material having light transparency in a wavelength range of the light emitted from the light emitter, the insulating film disposed on the light transmissive electrocardiographic electrode is a light transmissive insulating film (20, 46) made of an insulating material having light transparency in the wavelength range of the light emitted from the light emitter, and wherein in operation the device is configured to illuminate the living body with the light emitted from the light emitter (8,9) through the light transmissive electrocardiographic electrode and the light transmissive insulating film, and the the light receiver is configured to receive light reflected by the living body. at least one pair of electrocardiographic electrodes (19, 24) for detecting electrical signals of a living body, insulating films (20, 25) disposed on the at least one pair of electrocardiographic electrodes (19, 24) and having one surfaces, which are positioned oppositely away from the other surfaces being in contiguity with the at least one pair of electrocardiographic electrodes (19, 24) and which serve as contact surfaces to be contacted with the living body, a light emitter (8,9) for emitting light to the living body, a light receiver for receiving the light emitted from the light emitter after being reflected by the living body, and a processing circuit (26, 52, 62) including an electrocardiographic signal detection unit (27, 53, 63) for generating an electrocardiographic signal by differentially amplifying the electrical signals of the living body, which are detected through capacitive coupling between the living body contacted with the contact surfaces of the insulating films (20, 25) and the at least one pair of electrocardiographic electrodes (19, 24), and a photo-plethysmographic signal detection unit for generating a photo-plethysmographic signal based on the light emitted from the light emitter (8,9) and the light received by the light receiver, characterised in that: at least one of the at least one pair of electrocardiographic electrodes (19,24) is a light transmissive electrocardiographic electrode (19, 43) made of an electroconductive material having light transparency in a wavelength range of the light emitted from the light emitter, the insulating film disposed on the light transmissive electrocardiographic electrode is a light transmissive insulating film (20, 46) made of an insulating material having light transparency in the wavelength range of the light emitted from the light emitter, and wherein in operation the device is configured to illuminate the living body with the light emitted from the light emitter (8,9) through the light transmissive electrocardiographic electrode and the light transmissive insulating film, and the the light receiver is configured to receive light reflected by the living body. at least one of the at least one pair of electrocardiographic electrodes (19,24) is a light transmissive electrocardiographic electrode (19, 43) made of an electroconductive material having light transparency in a wavelength range of the light emitted from the light emitter, the insulating film disposed on the light transmissive electrocardiographic electrode is a light transmissive insulating film (20, 46) made of an insulating material having light transparency in the wavelength range of the light emitted from the light emitter, and wherein in operation the device is configured to illuminate the living body with the light emitted from the light emitter (8,9) through the light transmissive electrocardiographic electrode and the light transmissive insulating film, and the the light receiver is configured to receive light reflected by the living body.