like spacer 1 from above to below whereby the offset ring like portions 1a are inserted between the louvers l thereafter a step of reducing the distance between the louvers as represented by a step s2 in fig1 is executed as mentioned above the blinds b expanded to a maximum extent are raised up to reduce the distance between the louvers b in conformance with a manner of usage thereof since the offset ring like portions 1a of the coil spring like spacer 1 are inserted between the vertically adjacent louvers l as shown in fig2 the distance between the louvers is reduced to a dimension of 2 mm corresponding to a diameter of the wire constituting the offset ring like portion fig5 shows this state first as represented by the step s3 in fig1 the blind b is put in the bath main body 2a of the washing bath 2 so that it is washed therein the washing liquid 5 is preliminarily put in the bath main body 2a of the washing bath 2 and the heaters 2d are activated to hold the washing liquid 5 at a temperature of 40 u00b0 c while the foregoing state is maintained the blinds b are held on the arms 4a of the pair of stands 4 as shown in fig8 and are dipped in the bath main body 2a of the washing bath 2 so as to allow the washing bath 2 to perform a washing operation in this case the recirculating pump 2c is operated.