Interconnection and damping assignment passivity-based control (IDA-PBC) provides a general framework to stabilize underactuated mechanical systems by assigning the desired Hamiltonian to the system, which is obtained from the solution of partial differential equations. In this article, the IDA-PBC method is applied to an underactuated cable-driven robot to stabilize out-of-plane motion of the system. An adaptation law for the system's mass is designed such that asymptotic stability is ensured with positive tension in cables through the direct Lyapunov method. The results are verified through some simulations.