To solve a problem of not sufficiently improving buckling resistance property of an electric resistance welded tube by conventional technology.
In the manufacturing method of the electric resistance welded tube, a steel strip is roll formed while it is being passed, both abutted ends of the strip in a width direction are electric-resistance-welded to form a tube 10, heat treatment is applied to an electric resistance welded area, and then the tube is straightened. When straightening the tube, a rotary straightening machine 8 is used wherein distance between the stands of the rotary straightening machine is set to satisfy the range defined by a formula: LDtanA, wherein L is the distance between the strands of the rotary straightening machine, D is the outer diameter of the tube, is a circular ratio, is the roll inclination angle of the rotary straightening machine, and A is a number within a range of (N/2)0.025.
KENMOCHI KAZUHITO
SAKATA TAKASHI
TSUBOUCHI SUSUMU
SAKASHITA SHIGETO
