Abstract: Provided is a device which effectively improves obstructive sleep apnea syndrome (OSAS), which places a small psychosomatic burden on the patient, and which is unlikely to cause a decrease in compliance or adverse side effects. The tongue position controller of the present invention includes: a mounting portion composed of a splint applied to a lower jaw dentition, and a capsule which is arranged on an inner curved portion of an upper surface of the splint, which is composed so as to cover at least a portion of a tongue when the splint is applied to the lower jaw dentition, and which has a through hole positioned at a tip of the tongue when the splint is applied; a pressure generating device that generates a negative pressure; and a tube that connects the through hole and the pressure generating device.