A printed circuit board is disclosed. The printed circuit board includes a first board unit and a second board unit disposed with a gap in-between, and a flexible optical board configured to transmit optical signals, which has one side stacked on the first board unit and the other side stacked on the second board unit, where the flexible optical board includes a core through which the optical signals travel, a cladding surrounding the core, and a circuit pattern buried in the cladding which transmits electrical signals. By forming the rigid boards and the flexible optical board as an integrated structure, the need for separate connectors is obviated, and thus the cost of the product can be lowered.