Manufacturing method of casing

A manufacturing method of a casing that includes a casing body which is formed in a tubular shape that is centered on and extends along an axis, and a suction nozzle and a discharge nozzle which protrude from the casing body toward an outer side in a radial direction of the casing body about the axis as a reference and communicate with an inside of the casing body, the method comprising:

• a step of preparing a casing forming member that includes a casing body forming portion which is formed in a tubular shape and a protruding portion forming portion which protrudes from the casing body forming portion toward the outer side in the radial direction;
• a step of placing the casing forming member on a table which is rotatable about a table axis which extends in a vertical direction and disposing a tool which is rotatable about a tool axis on an inner side of the casing forming member in the radial direction;
• and
• a step of forming the casing by performing cutting an inner circumferential surface of the casing forming member with the tool while rotating the table about the table axis together with the casing forming member and rotating the tool about the tool axis.