45 the nylon threads 45 lie parallel in the plane of each belt with an interval between one another the nylon threads 45 are formed from nylon 6 or nylon 66 while the rubber 46 is formed from natural rubber or styrene butadiene rubber the thickness of each synthetic fiber belt 47 is set within a range of 0 6 to 1 2 mm while its width is set within a range of 200 to 500 mm preferably within a range of 300 to 400 mm the synthetic fiber belts 47 of the first and the second reinforcing layers 41 42 extend helically about the axis of the tube in a first direction and in a second opposite direction respectively in the same manner the synthetic fiber belts 47 of the third and the fourth reinforcing layers 43 44 extend helically in opposite directions as shown in fig1 the dimension ratio of the diameter of the outer surface 244 hereinafter referred to as outer diameter u03c6 1 and the diameter of the inner surface 243 hereinafter referred to as inner diameter u03c6 2 of the elastic tube 24 u03c6 2 u03c6 1 is set within a range of 0 56 to 0 72 the elastic tube 24 is thus squeezed in an optimal manner as shown in fig5 during an initial period of squeezing by the squeezing rollers 22 the basis for selecting the dimension ratio will hereafter be described an experiment was performed using a first elastic tube and a second elastic tube to move concrete therethrough the first elastic tube had an outer diameter u03c6 1 set at 159 0 mm and an inner diameter u03c6 2 set at 101 6 mm the second elastic.