The optical device comprises a first substrate 10 having a control circuit formed on; optical waveguide layer 40 formed above the first substrate and having a refractive index changed by electro-optic effect; and second substrates 14a, 14b having prism electrodes 18 for applying voltages to the optical waveguide layer. The control circuit and the prism electrodes are electrically connected to each other via columnar conductors 20. Even in a case where thermal expansion coefficients of the control substrate and of the light deflection substrates are very different from each other, the pins are flexed corresponding to eternal forces, whereby junction is protected from being damaged in the joining processing. Thus, the optical switch can be highly reliable.