To provide a locking mechanism of a dental instrument hose in which an instrument hose is automatically locked when pulling out an instrument from an instrument holder by a desired length.

The locking mechanism of the dental instrument hose secured to the instrument holder of the type which shows that the instrument hose 4 is hung from the instrument holder 2 and suppresses the returning force by the self weight of the instrument hose. The locking mechanism has a lock mechanism 12 arranged in the instrument holder 2 and locking and unlocking the pass of the instrument and a sensor 11 detecting the moving and stopping of the instrument hose, and locks the instrument hose by operating the lock mechanism 12 when the sensor 11 detects the movement stop of the instrument hose 4 after the instrument 3 is pulled out from the instrument holder 2.