A connection server is a connection system that is able to perform communication with a plurality of user side terminals and establishes a connection between the user side terminals, and includes a passcode generator that generates and transmits a passcode to the user side terminal, a passcode storage unit that stores a passcode in association with the user side terminal, a passcode receiving unit that receives a transmission passcode from the user side terminal, a passcode authentication unit that determines whether there is a stored combination of passcodes that matches a combination of a generated passcode and a received transmission passcode, and a connection unit that establishes a connection between the user side terminals in response to the determination.