PURPOSE: To improve uniformity of coated oil in the width direction of a metal strip, by setting a diameter of sprayed oil droplet in a range of 30W15μm and changing a rotational speed of a bell in a specific manner in proportion to the transfer speed of the metal strip in a bell type electrostatic oil coating process for the metal strip.

CONSTITUTION: A metal strip 1 is slit at a slitter 8, coated with oil at an electrostatic oil coating device 9 and then wound round a winder 3. In this arrangement, a strip speed detector 11 to detect the rotational speed of a roller 10 in rotatable contact with the strip 1 is provided, from which detected signals are sent to a computing element 12. A first output from this computing element 12, i.e. voltage signal, is sent to an oil quantity controller 13 to regulate oil quantity, while a second signal from the computing element 12, i.e. voltage signal, is sent to an air quantity controller 15 to regulate the air flow rate to rotate a bell. And the bell is rotated at a high constant speed N1 in a low transfer speed region of the strip 1, whereas at a low constant speed N2 in a high transfer speed region of the strip 1; wherein N1 and N2 are set so that the diameter of sprayed oil droplet becomes 30μm or more and 150μm or less respectively and further the rotational speed of the bell is reduced from N1 to N2 gradually as the transfer speed increases.