Electron beam-confining electromagnets of an electron beam generator are aligned with an electron beam axis, each of the electromagnets being folded to define a main section and a pair of angled wing sections disposed at respective angles relative to said main section, and a conductor wound around the edge. An upper cladding layer is formed on the active layer, having a refractive index lower than that of the active layer. The retainer ring has a subordinate retainer member having a ring portion and a plurality of fins extending from the ring portion to retain the peripheral surface of the wafer. A third calculator decides a soft value of a first demodulated symbol by subtracting the distance 2a from a level Xk of the in-phase component Xk. A second conductor film is formed on the side face of the second insulation film.