An optical device (10) includes a joining structure in which a first conductive film (110) and a second conductive film (130) are joined to each other. The first conductive film (110) that constitutes the joining structure is constituted by a conductive material. The second conductive film (130) that constitutes the joining structure is constituted by a metal material. Apart of the second conductive film (130) comes into contact with the first conductive film (110). A plurality of concave portions are provided in a contact surface of the second conductive film (130) which comes into contact with the first conductive film (110). The contact surface has a surface roughness greater than a surface roughness of a non-contact surface of the second conductive film (130) which does not come into contact with the first conductive film (110).