PURPOSE: To reduce the generation of heat and to change a wavelength of a laser beam by changing the strength of a magnetic field to be impressed on a semiconductor laser element from a superconducting coil arranged near the semiconductor laser element.

CONSTITUTION: A semiconductor laser element 2 and a superconducting coil 1 are fixed to a heat sink 4 to be adjacent to each other. The superconducting coil 1 controls a magnetic field to be impressed on the semiconductor laser element 2 and changes a wavelength of an output laser beam. Accordingly, a problem of the generation of heat is hardly caused. A composite oxide superconductor to be used for the superconducting coil 1 is expressed by Formula (1) (where α is a group IIa element in the periodic table, β is a group IIIa element in the periodic table, γ is one element selected from a group Ib, a group IIb, a group IIIb, a group IVb and a group VIIIa elements in the periodic table and x, y and z are numbers satisfying the following conditions: 0.1≤x≤0.9, 0.4≤y≤3.0 and 1≤z≤5). This composite oxide is composed mainly of a perovskite oxide or a pseudoperovskite oxide.