A luer-lock type cylindrical tip (1) of a syringe (2) has a luer tip (7) of which a center portion is fitted with an injection needle (4) and a luer-lock portion (8) which is disposed outside the luer tip with a gap therebetween and which has a lock screw (8a) disposed therein. The lock screw is formed as a trapezoid screw having a root diameter H set to the range of 8.0 mm ± 0.1 mm, an inner diameter J set to the range greater than or equal to 6.6 mm and smaller than 6.8 mm, and a pitch P set to the range greater than 2.5 mm and smaller than or equal to 2.8 mm. Accordingly, it is possible to reliably prevent the injection needle from being loosened or pulled out in the handling process. It is also possible to easily replace the syringe needle with another one having different size at the time of use.
