To adjust a warning sound to be outputted to outside a vehicle.

When a sound collection unit 930 collects an environmental sound around a vehicle CR, an environmental sound acquisition block 730 acquires information on a second spectrum of the environmental sound collected by the sound collection unit 930. A production block 750 adjusts the level of a peak, which is found in a band of frequencies falling below a predetermined frequency in a first spectrum of a sound directly obtained from sound source data, into a level equivalent to a level obtained by adding up the second spectrum and a correction spectrum, and adjusts the level of a peak, which is found in a band of frequencies equal to or higher than the predetermined frequency in the first spectrum, into a level equivalent to the second spectrum. The production block 750 determines a result of adjustment, which is performed on the first spectrum, as a shape of a third spectrum, and produces an outside output sound signal having the shape of the third spectrum.