A slitter line for a metal strip, comprising a disposing device of shaft-body insertion objects, the disposing device comprising: an expansion/contraction shaft which is disposed at a predetermined position in the slitter line of the metal strip and formed in a tubular shape, having an outer circumference surface which is constituted so as to expand and contract freely on a cross section when viewed in a longitudinal direction; a holder which has an inner circumference which can be fitted outside the outer circumference surface of the expansion/contraction shaft; a ring member which is formed with an approximately doughnut-shaped thin plate and integrated with the holder; a disposing device main body which is capable of moving approximately in parallel along the expansion/contraction shaft; a chuck pedestal which is attached to a driving portion of an arm of a separator disposing portion and is fixed to an air cylinder; a piston which is formed in a rod shape, with one end thereof being connected to the air cylinder and the other end thereof being constituted so as to expand and contract freely to the side of the expansion/contraction shaft; a chuck base fitted to the chuck pedestal and fixed to the other end of the piston; and a chuck tip which is installed on a side opposite to the piston of the chuck base and also capable of being in contact with an outer circumference surface of the holder in association with expansion of the piston, having a cross section which is formed in a recessed manner when viewed from a shaft center direction of the expansion/contraction shaft, wherein the slitter line is constituted so that a contact pressure imparted to the outer circumference surface of the holder can be controlled when the chuck tip comes into contact with the outer circumference surface of the holder, wherein a pressure imparted by a chuck portion in contact with the outer circumference surface of the holder can be adjusted in a range of 0 to 0.4 MPa by adjusting an air pressure of the air cylinder. an expansion/contraction shaft which is disposed at a predetermined position in the slitter line of the metal strip and formed in a tubular shape, having an outer circumference surface which is constituted so as to expand and contract freely on a cross section when viewed in a longitudinal direction; a holder which has an inner circumference which can be fitted outside the outer circumference surface of the expansion/contraction shaft; a ring member which is formed with an approximately doughnut-shaped thin plate and integrated with the holder; a disposing device main body which is capable of moving approximately in parallel along the expansion/contraction shaft; a chuck pedestal which is attached to a driving portion of an arm of a separator disposing portion and is fixed to an air cylinder; a piston which is formed in a rod shape, with one end thereof being connected to the air cylinder and the other end thereof being constituted so as to expand and contract freely to the side of the expansion/contraction shaft; a chuck base fitted to the chuck pedestal and fixed to the other end of the piston; and a chuck tip which is installed on a side opposite to the piston of the chuck base and also capable of being in contact with an outer circumference surface of the holder in association with expansion of the piston, having a cross section which is formed in a recessed manner when viewed from a shaft center direction of the expansion/contraction shaft, wherein the slitter line is constituted so that a contact pressure imparted to the outer circumference surface of the holder can be controlled when the chuck tip comes into contact with the outer circumference surface of the holder, wherein a pressure imparted by a chuck portion in contact with the outer circumference surface of the holder can be adjusted in a range of 0 to 0.4 MPa by adjusting an air pressure of the air cylinder.