The second candidate is resistive plate chambers (RPCs). Large area RPC systems are used by experiments at B-Factories [4,5], and will also be used by experiments at LHC [6,7]. Such a large area RPC system can be constructed with a very low cost, because of their simple structure with no wires. The RPC can be very thin, for example, the total thickness of an RPC doublet for the BELLE KLM detector is only 3.2 cm. The position resolution is determined by the dimensions of readout cathode strips, and a resolution of 1 cm can easily be achieved. RPC is a very promising candidate for the JLC muon detector.