PROBLEM TO BE SOLVED: To provide a biological information detector and the like which can detect proper biological information when a contact condition of a contact surface with a subject changes or the like.SOLUTION: A biological information detector includes: a detecting part which has a light receiving part 140 for receiving light from a subject； a translucent member 30 which is provided at a case surface side that comes in contact with the subject of the biological information detector, transmits light from the subject, and comes in contact with the subject when measuring biological information of the subject； and diaphragm parts 80 and 82 which are provided between the translucent member 30 and the detecting part, between the translucent member 30 and the subject, or in the translucent member 30, and narrow the light from the subject in an optical path between the subject and the detecting part.
