PURPOSE: To provide a working method of the housing of a screw type pump which can make the axes of a bottom member, a lid member, and a bearing hole coincide at a high accuracy, and can force to deliver the air efficiently.

CONSTITUTION: By inserting a knock pin 33a to tentative assembling knock holes 10a and 10b, a block 31 to form a housing main body 1 and a bottom member 2, and a block 32 to form a lid member are connected integrally and assembled tentatively. To the block 31 and 32 assembled tentatively and fixed, a rotor housing hole 7 in which a male rotor and a female rotor are housed by unitary spindles 34 and 35; bearing holes 8a, 8b, 9a, and 9b to hold the rotary shafts of the male rotor and the female rotor; and assembling knock holes 3a and 3b to assemble the housing main body 1 and the lid member with spindles 38 are bored simultaneously. To the unitary spindles 34 and 35, plural bites are installed from the spindle of shorter rotary diameter in order from the lower side to the upper side of a single shaft.