PURPOSE: To transport optical glass blanks always to the specified position in a heating furnace.

CONSTITUTION: The thermal change in a pallet 12 by a temp. change in the preheating furnace 4 is measured by thermocouples placed at transporting rails 31 in the preheating furnace 4 and the deformation rate by the heat of the pallet 12 is calculated at the time of placing a gob tray 14 holding the optical glass blanks 15 on the pallet 13, transporting this tray into the preheating furnace 4, holding the gob tray 14 by means of transporting arms 18 and transporting the tray to a pair of upper and lower molds. The feed rate of the pallet is then controlled to be corrected according to the deformation rate calculated in such a manner, by which the gob tray 14 is supplied always to the specified position.