Au base electrode materials have fatal disadvantages, such as inferior adhesion to diamond, low mechanical strength, and low thermal stability.A diamond UV sensor is provided which includes a photoconductive or Schottky optical sensor element having two-terminal electrodes and detects light irradiating a light-receiving portion according to the changes in electrical resistance or photo-induced current of the material of the light-receiving portion. The sensor element includes diamond having a surface from which a conductive surface layer has been removed, and the surface of the diamond is used as the light-receiving portion and a junction interface with the electrodes. The electrodes include a rectifying and an ohmic electrode. The rectifying electrode is transparent electrode capable of transmitting light and is defined by a single layer made of a nitride of a refractory metal element. The ohmic electrode includes a first layer made of a reactive elementary metal that can react with diamond to form a carbide or a carbon-containing solid solution, and a second layer made of a nitride of a refractory metal element.