A sound increase apparatus includes a partition wall adapted to divide an engine room for defining a first engine room space that is located on a side of a dash panel and a second engine room space in which an engine is installed, and a first pressure fluctuation amplification unit inter-communicating an engine inlet pipe arranged in the second engine room space and the first engine room space. The first pressure fluctuation amplification unit amplifies a pressure fluctuation of a first frequency selected from a plurality of frequencies when pressure of air residing inside the engine inlet pipe fluctuates at the plurality of frequencies.