To provide an index device for an electric discharge machine installed in every type of an electric discharge machine regardless of being new or already installed new or existing by making the index device having an indexing mechanism compact and freely removable and an electric discharge machining method using it, reduced in operator's load, enabling unmanned operation, and inexpensive.

This index device for the electric discharge machine is installed in every type of the electric discharge machine regardless of being new or already installed, and constructed of a power supply, a power transmitting mechanism for transmitting the power of the power supply, and a workpiece holding part turned at a predetermined angle by the power transmitting mechanism and holding the workpiece. The index device is removably mounted on the electric discharge machine, and this electric discharge machining method uses it.