PURPOSE: To facilitate the mass-production of paper vessels provided with mouth plugs, by inclining a thermoplastic resin-coated paper vessel whose inclined surface has a position expected to be bonded with the mouth plug, by a fixed angle, heating the bonding-expected position, and pressing the mouth plug onto the heated position.

CONSTITUTION: A paper vessel A carried by a conveyer 11 is held through a star wheel 19 by the paper vessel holder 84 of a rotary member 22, while a mouth plug B fed from a shoot 23 is set along a fixed direction by a positioning means 24, carried to the rotary member 22 by carrier discs 25, 26 and arranged on the paper vessel A. Thereafter, with the rotation of the rotary member 22 along the direction shown as the arrow, the paper vessel A is inclined so that an inclined surface, onto which the mouth plug B is expected to be bonded, is kept horizontally. An arm 88 is then rotated around a shaft 87 to interpose a heater 86 at its top end between the paper vessel A and the mouth plug B. Thus, the parts of the vessel A and the plug B to be bonded are heated. Thereafter, the heater 86 is retreated, and the paper vessel A and the mouth plug B are pressed and bonded together. The product is discharged through a star wheel 89 onto a conveyer 90.