To make it possible to flexibly set a power source voltage supplied to a constant current circuit according to an ambient temperature and to set a non-selection voltage at an adequate value independently from the power source voltage supplied to the constant current source.

A control circuit 31 reads the set value meeting the temperature detected by a temperature sensor 4 from LUT 1 and LUT 2. The circuit outputs the set value read out of the LUT 1 to an electronic volume control 226 and outputs the set value read out of the LUT 2 to an electronic volume control 126. A power source circuit 22 for generating the power source voltage supplied to the constant current source and a power source circuit 22 generating the non-selection voltage respectively change the output voltage according to the changes made by the resistance values of the electronic volume controls 226 and 126 changed in the set values.

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