In the present invention, a lubricant supplying device includes a lubricant end determining unit that determines that a solid lubricant is in an end state when the amount of a lubricant supplying operation reaches a threshold after a residual amount detecting unit detects that the residual amount of the solid lubricant is equal to or smaller than a predetermined amount. The lubricant end determining unit makes a threshold of the amount of the lubricant supplying operation at temperature or humidity of equal to or lower than a predetermined value lower than a threshold of the amount of the lubricant supplying operation at temperature or humidity of higher than the predetermined value.