To provide an aid for sterilizer for medical instrument, in which even an instrument such as a scaler as a dental instrument having a sharpened part such as blade or gimlet on the top end of a slender handle part can be safely and stably installed.

This aid is composed of a horizontal holding plate 14 having a vertical plate flange 15 as a component to be provided on the front side of an inserting port 9 and a holder 17 formed with a lock groove 18 to the vertical plate flange 15 along with the outer peripheral part of an inserting port part 25 of a cylinder 16 into which the medical instrument to be sterilized is partially inserted.