To regulate the projection level of tools from toolholders of a shrinkage fit type accurately and adjust the limitation level accurately and easily, via simple construction.

This regulator 20 limits tool insertion travel L1 into a toolholder 10 having a chuck portion 12 for holding a tool shank with a shrinkage fit. The regulator 20 comprises a limiting rod 21, an adjusting member 22 and a holding member 25. The holding member 25 has an external thread 26a that can be put in threaded engagement with an internal thread 13a in a center bore 13 of the toolholder 10. The limiting rod 21 and adjusting member 22 are fixed together, and rotating the adjusting member 22 determines the tip position of the limiting rod 21 to regulate the insertion travel L1.