A fine pattern, such as a semiconductor integrated circuit, a liquid crystal panel, and a photomask for the semiconductor or the liquid crystal panel, which are fabricated based on data for fabricating the fine pattern such as design data is inspected by a pattern inspection apparatus. In one aspect, a drive system of a self-propelled machine incorporating engine stall protection includes an engine being in communication with a control unit and transmitting power and an engine load signal to the control unit. The hook member has a hook section provided thereon, such that when the ceiling panel is positioned within the grid network, the hook section and a grid flange cooperate to accurately position the panel relative to the grid network. The hot plate is clamped between the holding ring and the seal element. The invention uses a PLC as its basic structure and applies the principle that the product of the number of output optical waveguides and the channel spacing is equal to the free spectral range of the spectrum of any output optical waveguide to make a compact PLC interleaver.