Disclosed is a foreign substance removing device for a dental unit chair. The present invention comprises: first and second cyclone gas-liquid separators； a first inhale pipe； a second inhale pipe； a first intake pipe； a second intake pipe； and a vacuum breaking unit. Each of the first and second cyclone gas-liquid separators includes a cone unit in which a foreign substance discharging unit is formed in a lower end unit. The first inhale pipe connects the circumference of an upper end unit of the first cyclone gas-liquid separator and a suction tip of the dental unit chair. An inlet of the second inhale pipe is connected to the first inhale pipe through a first three-way valve. An outlet of the second inhale pipe is connected to the circumference of the upper end unit of the second cyclone gas-liquid separator. The first intake pipe connects an upper part of the first cyclone gas-liquid separator and a vacuum pump air inhale unit of a suction device. An inlet of the second intake pipe is connected to an upper part of the second cyclone gas-liquid separator. An outlet of the second intake pipe is connected to the first intake pipe through a second three-way valve. The vacuum breaking unit selectively breaks vacuum of the first and second cyclone gas-liquid separators. The vacuum breaking unit includes: a vacuum breaking pipe； and a third three-way valve. One end of the vacuum breaking pipe is connected to the first inhale pipe to be positioned in a back side of the first three-way valve. The other end of the vacuum breaking pipe is connected to the second intake pipe. The third three-way valve is installed in the vacuum breaking pipe； and selectively connects one of the first and second cyclone gas-liquid separators to the atmosphere. The present invention is provided to completely separate foreign substances such as saliva, bloody pus, etc. received from a mouth of a patient from air； and to prevent pollution of z vacuum pump, thereby inhibiting damage of the vacuu
