A method for manufacturing a pipe with different diameters along a longitudinal direction that has a small diameter portion, a large diameter portion, and a diameter-changing portion provided between the small diameter portion and the large diameter portion and is formed by press forming a blank made of a metal sheet, the method comprising: a step of press forming the blank with a U-shape forming die set into a U-shaped formed part having a U-shape cross-section including a pair of vertical walls and a step of press forming the U-shaped formed part with an O-shape forming die set into a circular cross-section formed part, wherein: the U-shape forming die set includes a lower die, the lower die includes a forming surface that forms a U-shaped inner cross-section having a pair of vertical walls, a length of the vertical walls of the lower die is longer than a length of the vertical walls of a corresponding portion of the U-shaped formed part; and the O-shape forming die set includes a lower die in which the U-shaped formed part is set and an upper die to which the vertical walls of the U-shaped formed part contact, each of the lower die and the upper die includes a forming surface having an arc portion that forms a circular inner cross-section when the upper die and the lower die are mated at die mating lines and the die mating lines in a cross-sectional view are inclined downwardly from the inner cross-section when the lower die is mated with the upper die, a ratio t/D of a sheet thickness t of the blank to a diameter D of the circular inner cross-section at each of portions of the O-shape forming die set corresponding to the small diameter portion and the large diameter portion, is 0.010 ≤ t/D ≤ 0.080, and a circumferential compressive strain given by the following expression is equal to or more than 0.5%: Circumferential compressive strain = ( blank width in sheet width direction that becomes pipe circumferential direction − perimeter of die set) / perimeter of die set × 100 %. a step of press forming the blank with a U-shape forming die set into a U-shaped formed part having a U-shape cross-section including a pair of vertical walls and a step of press forming the U-shaped formed part with an O-shape forming die set into a circular cross-section formed part, wherein: the U-shape forming die set includes a lower die, the lower die includes a forming surface that forms a U-shaped inner cross-section having a pair of vertical walls, a length of the vertical walls of the lower die is longer than a length of the vertical walls of a corresponding portion of the U-shaped formed part; and the O-shape forming die set includes a lower die in which the U-shaped formed part is set and an upper die to which the vertical walls of the U-shaped formed part contact, each of the lower die and the upper die includes a forming surface having an arc portion that forms a circular inner cross-section when the upper die and the lower die are mated at die mating lines and the die mating lines in a cross-sectional view are inclined downwardly from the inner cross-section when the lower die is mated with the upper die, a ratio t/D of a sheet thickness t of the blank to a diameter D of the circular inner cross-section at each of portions of the O-shape forming die set corresponding to the small diameter portion and the large diameter portion, is 0.010 ≤ t/D ≤ 0.080, and a circumferential compressive strain given by the following expression is equal to or more than 0.5%: Circumferential compressive strain = ( blank width in sheet width direction that becomes pipe circumferential direction − perimeter of die set) / perimeter of die set × 100 %. the U-shape forming die set includes a lower die, the lower die includes a forming surface that forms a U-shaped inner cross-section having a pair of vertical walls, a length of the vertical walls of the lower die is longer than a length of the vertical walls of a corresponding portion of the U-shaped formed part; and the O-shape forming die set includes a lower die in which the U-shaped formed part is set and an upper die to which the vertical walls of the U-shaped formed part contact, each of the lower die and the upper die includes a forming surface having an arc portion that forms a circular inner cross-section when the upper die and the lower die are mated at die mating lines and the die mating lines in a cross-sectional view are inclined downwardly from the inner cross-section when the lower die is mated with the upper die, a ratio t/D of a sheet thickness t of the blank to a diameter D of the circular inner cross-section at each of portions of the O-shape forming die set corresponding to the small diameter portion and the large diameter portion, is 0.010 ≤ t/D ≤ 0.080, and a circumferential compressive strain given by the following expression is equal to or more than 0.5%: Circumferential compressive strain = ( blank width in sheet width direction that becomes pipe circumferential direction − perimeter of die set) / perimeter of die set × 100 %.