Imaging is performed such that a flow-down path of the liquid from the nozzle arranged above a work to an upper surface of the work is included in an imaging field of view (Step S401). A total value of pixel values of pixels belonging to each pixel column composed of the pixels arranged in a line along a flow-down direction of the liquid in an evaluation region corresponding to the flow-down path out of an imaged image is calculated (Step S402-S403). Based on a change mode of the total value in an orthogonal direction orthogonal to the flow-down direction, presence or absence of the flow-down of the liquid is determined (Step S405-S407).