The wavelength control device comprises a first Mach-Zehnder filter which receives a first optical signal and outputs an optical signal having a predetermined wavelength, a second Mach-Zehnder filter which receives a second optical signal and outputs an optical signal having a predetermined wavelength, a heating unit heating respective parts of either one of the waveguides of the first and second Mach-Zehnder filters, a first wavelength detecting unit which receives an optical signal from the first Mach-Zehnder filter and detects a wavelength thereof, a second wavelength detecting unit which receives an optical signal from the second Mach-Zehnder filter and detects a wavelength thereof, a power control unit which controls power supplied to the heating unit based on the wavelength received from the first wavelength detecting unit, and an output unit which outputs a wavelength value based on the wavelength received from the second wavelength detecting unit.