PURPOSE: To surely prevent by belt from meandering by sliding a tension roller in a follow-up manner so as to press the belt end in an opposite side to a belt meandering direction when a meandering belt presses a meander detecting part, in the case of a belt meander-preventing device for a heat developing device or the like.

CONSTITUTION: When an upper belt 1 meanders, for instance, in a direction B, a belt guide 33 is pressed by an edge of the belt 1 to move a tension roller 21 in the direction B. Here in the tension roller 21, a side B is moved upward and a side A is moved downward by a guide pin 38 brought into slide contact with a guide part 36b of a guide 36 and by a guide pin 39 brought into slide contact with a guide part 37b of a guide 37. Accordingly, the belt 1 in the side A is pressed by the tension roller 21 and deflected to the side A to correct meandering.