To provide a current form conversion device for reducing the short- circuit current capacity of a converter, miniaturizing the converter, and improving economical efficiency by breaking only a short-circuiting current, without breaking a main circuit current.

Assume that a U-phase GTO (self-arc-extinguishing element) 5a is damaged, a short-circuiting current flows through a path of an AC S phase → a GTO 5b → a fuse 9b → a fuse 9a → the self-arc-extinguishing element 5a → an AC R phase (dotted lines). The short-circuiting current is quickly limited by the fuses 9a and 9b, and a converter is protected from an excessive short-circuiting current. A main circuit current needs to flow, while protecting a short-circuiting current. Therefore, a diode 10b is connected in parallel with the fuse 9b, so that the main circuit current flows through the diode 10b instead of the fuse 9b, even if the fuse 9b blows out.