A method for coating an object with a threadlike coating material using a coating device comprising: a rotary head to which a coating material is supplied; a drive unit that rotates the rotary head; and an electric power supply unit that applies a negative high voltage to the rotary head so as to form an electric field between the rotary head and a grounded object to be coated, wherein the rotary head includes a diffusion surface that is configured such that, when the rotary head is rotated by the drive unit, the coating material is diffused toward an outer edge portion of the diffusion surface by a centrifugal force, and a plurality of groove portions that are included in the outer edge portion, wherein the coating material reaching the outer edge portion is supplied to the groove portions and becomes threadlike when passing through the groove portions, the rotary head discharges the threadlike coating material from the groove portions, the threadlike coating material discharged from the rotary head being atomized by an electrostatic force to form coating material particles which are applied to the object to be coated to form a coating film on a surface of the object to be coated, characterized in that a diameter of the threadlike coating material is set equal to or larger than 0.03 mm and equal to or smaller than 0.1 mm, and a dimension of the threadlike coating material is set based on a flow rate of the coating material supplied to the rotary head and a rotational speed of the rotary head, wherein the flow rate of the coating material supplied to the rotary head is 10 to 300 cc/min and the rotational speed of the rotary head when the coating material is discharged is 10000 to 30000 rpm. a rotary head to which a coating material is supplied; a drive unit that rotates the rotary head; and an electric power supply unit that applies a negative high voltage to the rotary head so as to form an electric field between the rotary head and a grounded object to be coated, wherein the rotary head includes a diffusion surface that is configured such that, when the rotary head is rotated by the drive unit, the coating material is diffused toward an outer edge portion of the diffusion surface by a centrifugal force, and a plurality of groove portions that are included in the outer edge portion, wherein the coating material reaching the outer edge portion is supplied to the groove portions and becomes threadlike when passing through the groove portions, the rotary head discharges the threadlike coating material from the groove portions, the threadlike coating material discharged from the rotary head being atomized by an electrostatic force to form coating material particles which are applied to the object to be coated to form a coating film on a surface of the object to be coated, characterized in that a diameter of the threadlike coating material is set equal to or larger than 0.03 mm and equal to or smaller than 0.1 mm, and a dimension of the threadlike coating material is set based on a flow rate of the coating material supplied to the rotary head and a rotational speed of the rotary head, wherein the flow rate of the coating material supplied to the rotary head is 10 to 300 cc/min and the rotational speed of the rotary head when the coating material is discharged is 10000 to 30000 rpm.