The coating instrument is provided with a coating head which has a plurality of head members, and in which a groove-like slot is formed, an adjustment unit accommodated in a recessed groove installed on a leading end face continuing to an outer face opposite to an inner face or to the inner face in the head member to adjust the width of the slot by pressing a side wall face of the recessed groove, and a controller for controlling a pressing force to the side wall face of the recessed groove by the adjustment unit. The adjustment unit is provided with a fluid pressure chamber into which a fluid is sealed, a pressing portion for pressing the side wall face of the recessed groove by the fluid pressure of the fluid pressure chamber, and an operating portion for allowing the fluid pressure of the fluid pressure chamber to change. The controller is provided with a pressure detecting portion for detecting the fluid pressure of the fluid pressure chamber and an instruction portion for comparing the fluid pressure detected by the pressure detecting portion with a previously-set pressure range to give instructions to the operating portion.