A bike carrying device includes a support post (5), a mounting unit (4) mounted on the support post, a positioning bar (6) mounted on the mounting unit, a pawl member (7) mounted in the mounting unit, a release member (415) mounted in the mounting unit, a lock mechanism (414) mounted on the mounting unit and connected with the release member, and an elastic member (8) biased between the mounting unit and the pawl member. Thus, the bike carrying device has a simplified construction to decrease the cost of fabrication.