PURPOSE: To provide effective use of a surging energy absorption device throughout a year by inserting and drawing out a back plate at the rear open part and changing over from a position to receive surges in one direction to another position to receive surges in the opposite direction or vice versa according to the condition of surging.

CONSTITUTION: An oscillating plate 12 for absorption of surging energy is installed in the middle part of a caison 10, and through its rotary shaft 13 the oscillator 12 moves in linkage with an oil pressure generator 14 installed at the caison 10. At both open parts 11A, 11B are installed back plates 16A, 16B, which can be inserted and drawn out under guidance of grooves 15A, 15B formed vertieally in the caison 10, where insertion and drawing-out is operated by oil- hydraulic cylinder devices 17A, 17B, which can be changed over in accordance with the condition of surging. Thus the surging energy can be absorbed effectively.