A secure star coupler in a communication network adopting a time-triggered protocol based on a time slot include: transceivers each of which is connected to one of branches and transmits and receives signals; a routing table holder that holds a predetermined rule indicating a correspondence between a time slot and a branch; and a router that routes a signal received from a first branch to another branch unless a no-transfer condition is satisfied. The no-transfer condition includes a condition that the predetermined rule is not followed by the first branch and a condition that routing of a signal received from a second branch different from the first branch has started in the time slot.