Communications are established between a referring content and a referred content. A content providing server 1 includes an obtainer 11 configured to obtain first post data P1 from a first user terminal 3 on which first content data M1 is being viewed, and second post data P2 from a second user terminal 4 on which second content data M2 is being viewed; and an output unit 12 configured to output the first content data M1 and the first post data P1 to the first user terminal 3, and the second content data M2 and the second post data P2 to the second user terminal 4, and to output, if referring to and outputting the second content data M2 on the first content data M1, the second content data M2 to the first user terminal 3, and the first post data P1 to the second user terminal 4.