An intercept system includes: a call controller that controls a call between a plurality of communication devices connected through a packet network; a route setting device that sets a route along which communication on a call between the communication devices is relayed; a duplicating device that duplicates a packet to be intercepted; an acquiring unit that acquires communication device identification information for identifying positions on the packet network of the communication devices from the call controller; a setting unit that sets the route setting device in such a way that a packet received from one communication device is transmitted to the duplicating device as to communication on a call between the communication devices identified by acquired communication device identification information; and a returning unit that returns a received packet to the route setting device after duplicating the received packet by the duplicating device for use in interception.