as to seal off the space between the respective end portions 4a of the spacer members 4 from outside with welding material used in the welding method thereby to form a welded portion 14 thus by the welded portion formed at the end of each screen jacket 12 the seal means is constituted the surface of the welded portion should preferably be formed on the same plane as the surface of the jacket by doing so smooth filling of gravel can be facilitated it is important in making a well to fill gravel uniformly in the annulus defined between the wall of the wellbore and the outer surface of the screen if the outer surface of the screen between adjacent screen jackets 12 12 is recessed from the surface of the screen jackets 12 12 the gravel is sometimes not filled in this recess so that a hollow portion is produced in the gravel filled in the annulus between the wall of the wellbore and the outer surface of the screen this hollow portion is later filled with gravel which has transferred from around the hollow portion by either pumping of oil or pressure difference in the well but this in turn tends to cause collapse of the wall of the wellbore resulting in reduction in the oil production efficiency in the present embodiment of the invention the surface of the welded portion 14 or the surface of the sleeves 6 and 26 in the embodiment of fig1 and 6 is formed on the same plane as the screen jackets and accordingly smooth filling of gravel is ensured and occurrence of production of the hollow portion in the gravel layer can be effectively.