To lessen the odd feel during use and to surely prevent the retreat of the mandible during sleeping.

This jaw fixing device 1 is composed of a fixing piece 2 and a fillet 3. This fixing piece 2 is formed to a nearly H shape in section having an outside wall part 4, an inside wall part 5 and a partition wall part 6 and has accepting grooves 7, 8 which accept part of the dental arch in the upper part and lower part of the partition wall 6. A through hole 12 in a vertical direction is formed at the partition wall 6. The filler 3 is a compsn. which is harmless to the human body and rapidly changes from a pasty state of a high viscosity to a gelatinous state having elasticity. The fixing piece 2 packed with the filler 3 is bitten by the upper and lower teeth and the upper and lower teeth are coupled by the solidification of the filler 3, by which the retreat of the mandible is prevented.