Herein disclosed are screw rotor tooth profile which comprises a pair of male and female rotor tooth profiles engaging each other. The screw rotor tooth profile is configured such that at least one of the male and female rotor tooth profiles has a point of minimum pressure angle or an engaging tooth surface concurring with those of a theoretical tooth profile and is deviated from the theoretical tooth profile such that the amount of deviation increases as going from the point of minimum pressure angle or the engaging tooth surface toward the tooth top side and the tooth bottom side. The screw rotor tooth profile, even in case of the presence of machining and/or assembling errors in the profiles. are capable of assuring excellent mutual tooth engagement therebetween and almost not susceptible to that or those errors, that is, insensitive to precision.
