PURPOSE: To enable free adjustment and setting of the conveying speed of a material which is to be heated and is conveyed in a furnace by dividing a stationary hearth to each of a preheating zone, heating zone and soaking zone and making a part or the whole of the divided stationary hearths variable to the upper positions from the rising limit of movable hearths.

CONSTITUTION: A stationary hearth 9 of a walking furnace provided with the stationary hearths 9a, b, c and movable hearth 8 is divided to each of a preheating zone A, heating zone B and soaking zone C in a furnace body 1. The divided hearths 9a, 9b, 9c are normally in the home positions shown by solid lines and can be respectively independently made variable to the upper positions from the rising limit of the hearth 8 by driving devices 10a, 10b, 10c if necessary.