A vacuum pump comprising a thread groove pump mechanism (PB) including: a rotor cylinder portion provided in a rotor rotatable in a predetermined rotating direction; a substantially cylindrical stator disposed beside the rotor cylinder portion via a gap coaxially with the rotor cylinder portion; a plurality of ridge portions extended along a gas exhaust direction on either an opposite surface of the stator opposed to the rotor cylinder portion or an opposite surface of the rotor cylinder portion opposed to the stator; and a thread groove engraved between the plurality of ridge portions, the vacuum pump transferring gas in the thread groove from an intake side to an exhaust side in the gas exhaust direction, wherein : the vacuum pump includes gas retention suppressing means for suppressing retention of a gas in an exhaust side outlet of the thread groove, and the gas retention suppressing means is an inflow suppressing wall formed by widening an exhaust side end portion (71 b, 81b) of the ridge portions on the exhaust side in the gas exhaust direction greater than an intake side end portion of the ridge portions on the intake side in the gas exhaust direction, characterised in that the plurality of ridge portions comprises an equal width region (D, F) formed in a same width as the intake side end portion and a widened region (E, G) formed by widening to the exhaust side end portion to be contiguous with the equal width region and forming the inflow suppressing wall. a rotor cylinder portion provided in a rotor rotatable in a predetermined rotating direction; a substantially cylindrical stator disposed beside the rotor cylinder portion via a gap coaxially with the rotor cylinder portion; a plurality of ridge portions extended along a gas exhaust direction on either an opposite surface of the stator opposed to the rotor cylinder portion or an opposite surface of the rotor cylinder portion opposed to the stator; and a thread groove engraved between the plurality of ridge portions, the vacuum pump transferring gas in the thread groove from an intake side to an exhaust side in the gas exhaust direction, wherein : the vacuum pump includes gas retention suppressing means for suppressing retention of a gas in an exhaust side outlet of the thread groove, and the gas retention suppressing means is an inflow suppressing wall formed by widening an exhaust side end portion (71 b, 81b) of the ridge portions on the exhaust side in the gas exhaust direction greater than an intake side end portion of the ridge portions on the intake side in the gas exhaust direction, the vacuum pump includes gas retention suppressing means for suppressing retention of a gas in an exhaust side outlet of the thread groove, and the gas retention suppressing means is an inflow suppressing wall formed by widening an exhaust side end portion (71 b, 81b) of the ridge portions on the exhaust side in the gas exhaust direction greater than an intake side end portion of the ridge portions on the intake side in the gas exhaust direction, characterised in that the plurality of ridge portions comprises an equal width region (D, F) formed in a same width as the intake side end portion and a widened region (E, G) formed by widening to the exhaust side end portion to be contiguous with the equal width region and forming the inflow suppressing wall. <EOS>