Disclosed is a passive converter for a drive device of a switched reluctance motor (SRM), in which high demagnetization voltage for the SRM is provided. The converter includes a rectifier which smoothes input voltage to supply DC voltage, a boost circuit connected with the rectifier, and an asymmetric converter connected with the boost circuit, and the boost circuit includes first to third diodes and first and second capacitors. The high demagnetization voltage is generated at current duration of a single phase or poly-phase SRM by using the passive converter for the drive device of the SRM, so that the driving efficiency and the output power of the SRM can be increased.