A cross section of a tooth profile of a first screw rotor (17) perpendicular to the rotor axis includes a tooth top arc (A1B1), a tooth bottom arc (C1D1), a first curve (A1C1), and a second curve (B1D1). The first curve (A1C1) is a first trochoidal curve that connects a first end (A1) of the tooth top arc (A1B1) to a second end (C1) of the tooth bottom arc (C1D1). The second curve (B1D1) connects the second end (B1) of the tooth top arc (A1B1) to the first end (D1) of the tooth bottom arc (C1D1). The second curve (B1D1) is a composite curve formed by an involute curve (B1E1) and a second trochoidal curve (E1D1), which extend continuously from each other at a first intersection point (E1). A screw pump (11) thus suppresses leakage of fluid with improved performance.