To easily perform boring work by a tool when the tool is used alternately with a tool supporting device and without a tool supporting device in accordance with a working condition in boring.

This tool supporting device 1 comprises a magnet 4 magnetically attached to a metal surface 3, a base 5 projected from the magnet 4 extended in the vertical direction A with respect to the metal surface 3, and a tool supporting member 7 supported on the base 5 movably in the vertical direction A and supporting the boring tool 6. The tool supporting member 7 comprises a movable body 19 mounted in parallel with the base 5 extended toward the vertical direction A and supported by the base 5 movably to the vertical direction A, a supporting member body 21 mounted in parallel with the movable body 19 and fixing the tool 6, and a locking means 22 for locking and unlocking the supporting member body 21 fixing the tool 6 to the movable body 19.