A submerged tubular wave energy converter, whose main structure is an upright concentric circular cylinder, is proposed. The turbine is installed near the bottom of the internal tunnel for the survivability consideration. The analytical solution for the wave diffraction problem of the structure is derived based on the linear potential flow theory. The oscillatory mass flow rate in the tunnel is particularly investigated for it can be used to assess the feasibility of the converter that utilises the vertically oscillatory water flow. The effect of the submerged tubular structure in a wave field is to guide the vertically oscillatory motion, the magnitude of which, otherwise, diminishes exponentially with depth, down to the deeper water. That greatly increases the available kinetic energy for the turbine installed in the deep water. Effects of the parameters of the tubular structure on the efficiency of the device are also discussed. (C) 2017 Elsevier Ltd. All rights reserved.