PURPOSE: To make a dental instrument holder to be equipped for positioning a dental instrument to be used for dental examination on the lower side of the front of a dental tray table and retaining it, and make changeable into either of a hanger type or a tray type by simple operation.

CONSTITUTION: Each divided groovelike part 1a whose width is wider than the diameter of an instrument hose 9 and at least whose front and rear widths are narrower than the diameter of a holding part 10a of an instrument 10, is provided on the lower surface side of each penetration hole that holds surrounding the rear part of a dentist's instrument 10 and each engagement groove is provided on the rear side of each penetration hole part and at the same time a large opening part is provided in the state of being connected to each divided groovelike part 1a. Each approximately U shaped falling-out stop member whose width is narrower than the diameter of a connector part 9a or the holding part 10a of the instrument 10 and also whose width is wider than the diameter of the hose 9, is attachably/detachably engaged with each engagement groove, and each detecting means to detect the existence of the instrument 10 is equipped at the inside predetermined part of each penetration hole part.