Disclosed is a wireless communication system including: a controller and a plurality of communication terminals connected to each other for communication, and the controller includes: a first wireless communication section; a communication number control section which counts a communication number of each of the communication terminal communicated and stores the number in the storage section; and a first communication control section which sets back off information indicating priority of communication of the communication terminal according to the communication number stored in the storage section and transmits the back off information through the first wireless communication section to the communication terminal, and the communication terminal includes: a second wireless communication section; and a second communication control section which sets the back off time of communication with the controller shorter as the priority becomes higher based on the back off information received from the controller.