gap into the outside and an inner pressure is not increased as a result the piston 2 is prevented from being disengaged from the main body 1 due to an increase in the inner pressure fig3 to 7 show different embodiments of the piston favorably applicable to the cartridge type dispenser according to the present invention fig3 shows the piston 2 in which the protrusions 3 are provided at the end portions of the trunk portion 2 a of the piston 2 while a shape of the trunk portion 2 a remains cylindrical in this case contact of the piston 2 with the main body 1 is made at the protrusions 3 provided at a front end portion and a rear end portion of the piston 2 accordingly a contact area is further reduced and operability is further improved fig4 shows the piston 2 in which the protrusions 3 are provided in a portion of the trunk portion 2 a other than the end portions thereof while the shape of the trunk portion 2 a remains cylindrical in this case as in fig3 the contact area is further reduced and operability is further improved fig5 shows the piston 2 in which the single protrusion 3 is helically formed while the shape of the trunk portion 2 a remains cylindrical which shows an example of the smallest number of the protrusion still satisfying demand characteristics of the present invention fig6 and 7 show the pistons 2 in each of which the size diameter d in the middle portion of the trunk portion 2 a in a longitudinal direction thereof is minimized with respect to the sizes diameters d i d 2 d 1.