PURPOSE: To provide a manufacture of granular thermoplastic resin pellets and foamable thermoplastic resin particles possible to classify and having uniform quality by an extrusion method.

CONSTITUTION: A molten thermoplastic resin is extruded from a die to be cut by a cutter provided in a non-contact state with respect to the die and immediately immersed in a cooling medium to be cooled to obtain thermoplastic resin pellets having a circular or an almost circular shape in a plan view and a spindle shape or almost spindle shape in a front or side view. A foaming agent is infiltrated into the thermoplastic resin pellets.