PURPOSE: To obtain a lightweight tightening device having the superior workability by installing an elastic compressible body which is connected with each fixed plate and generates a compression force, supply/discharge means for the pressurized fluid, and a clamping means for holding a wire member.

CONSTITUTION: A clamping means 26 is operated to hold each wire member 14 passing through each cut part 16 on a fixed plate 12, and then a supply/discharge means 24 is operated to allow the pressurized fluid to flow into the inside space of each elastic compressible body 18, and then the elastic compressible body 18 expansion- deforms, and contracts in the axis line direction. Accordingly, the end parts of the wire members 14 are approached each other by the mutual approach of the fixed plates 12 due to the contraction movement of the elastic compressible body 18, and tightened until the end parts are superposed each other, and the preparation for the connection work for the wire member 14 is performed. When the connection work for the wire member 14 is completed, the supply/discharge means 24 is operated to open a conduit, and the pressurized fluid is discharged from the inside space of the elastic compressible body 18, and the tightening of the wire member 14 is released, and then fixed plate 12 is separated each other by the restoration of the wire member 14 and the elastic compressible body 18.