One of the treatments for obstructive sleep apnea syndrome (OSAS) is the use of an oral appliance (OA). Although many papers have shown a certain degree of effectiveness in treating OA, one of the drawbacks of the device is the discomfort and mental burden it causes when worn. One of the reasons for this is thought to be the feeling of restriction due to the type of OA that completely fixes the upper and lower jaws (fixed type OA) because the opening is completely restricted. On the other hand, there is also a type of device that allows opening movement (separate type OA), but with separate type OA it is necessary to attach a connector that connects the upper and lower jaw devices to the cheek side, and its protrusion feels more uncomfortable than fixed type OA. There is a possibility that this may occur. However, until now, there is little information on the extent to which there is actually a difference in the feeling of wearing or the mental burden of wearing a fixed type and a separate type. The purpose of this study is to clarify the feeling of wearing fixed OA and separate OA devices, as well as the differences in mental stress caused by wearing these devices.