A polyamide resin is produced by polycondensing a polyamide oligomer having a relative viscosity of from 1.1 to 1.3 and a water content of 3% by weight or less by melt-kneading using an intermeshed co-rotation twin screw extruder having at least one or more open vents OV1 and OV2 and at least one or more vacuum vents VV1 and W2. A pressure-decreasing element Y for increasing the resin filling rate is provided at a position nearer to the supply section side than positions at which the vacuum vents VV1 and VV2 are provided, and an area of 30% or less of the total screw length is a vacuum area having a pressure of 300 Torr or less.
