PURPOSE: To obtain a titled modulator having high reliability by disposing two sheets of etalon plates which are transparent to IR light in parallel at a slight space and fluctuating finely the space between the two plates according to the voltage to be impressed on piezoelectric elements.

CONSTITUTION: A piezoelectric element 40 is constituted of a piezoelectric wafer 41 and electrodes 43, 43. The electrodes 42, 43 on both surfaces of the wafer 41 are formed of vapor-deposited metallic films having 100W300°Cm.p. Both electrodes 42, 43 are so formed as to extend respectively to the edge and a part of the side face of the wafer 41, by which the electrodes are distributed respectively thereto. Plural sheets of the elements 40 having such constitution are superposed in a way as to permit impressing of voltage respectively in parallel therewith. When the element are thermocompression bonded by increasing the temp. to the m.p. of the vapor deposited metals or above, the respective superposed elements join to each other and the parts extending to the side faces of the elements 40 are connected to each other, whereby a pair of the electrodes 44, 45 having a comb-tooth section as shape are formed.