PURPOSE: To form a plate material of good workability to a conical shape by forming a driving roll and pressing roll both to a conical shape.

CONSTITUTION: A conical driving roll 5 is revolved and while the proximity degree of a conical pressing roll 10 is being adjusted by turning a screw rod 17, a sector form plate material is sent, whereby it is bent to a truncated conical shape such as the one shown by imaginary lines X. Since the driving roll 5 and pessing roll 10 are both formed to a conical shape, the peripheral speeds of the rolls are not uniform over the lengthwise direction and the peripheral speeds are higher as it goes closer to the rear part of the rolls, hence the conditions of feeding necessitating feeding the larger arc side of the sector form plate material faster than the smaller arc side may be satisfied. The secton-form plate material is readily bent to funnel form by the simple feed operation.