A plurality of speakers are installed at different positions in space and, of multichannel signals, only a center signal component is output from a speaker mounted in at least one seat located within the space. The modular decklid assembly includes a frame and a decklid that are installed in a vehicle as a modular unit. Whether or not the ejector plate 12 is normally moved is checked by monitoring waveforms of output values from the pressure sensor 27 before and after the movement of the ejector plate 12 at the ejection of a molded piece.