There is disclosed an optical fiber holding device comprising an optical fiber 1 with a grating 2 for reflecting a propagated optical signal of a number of wavelengths, a heater 3 for heating the grating 2 to a predetermined temperature distribution, a strip-shaped member 6 having a rectilinear groove in which the optical fiber 1 is accommodated, and the gel substance 7 contacting with the optical fiber 1 is filled, and a substrate 4 on which the heater 3 and the strip-shaped member 6 are mounted.