Authentication system in facility

An authentication system authenticating treatment based on a treatment order in a facility, the system comprising:

• a light source that emits illumination light including an illumination ID for specifying a location in the facility as information;
• a plurality of photoreceivers that transmit the illumination ID based on the illumination light and a prestored target ID when receiving the illumination light from the light source as data;
• and
• a processing unit that associates the photoreceivers located in an illumination area of the same light source based on the data transmitted from the photoreceivers, and then authenticates treatment by deciding whether a combination of the associated photoreceivers matches a combination of the photoreceivers based on the treatment order.