A support pin arrangement determination assisting method includes: displaying an image including a board image that indicates a shape and an arrangement of an already mounted component on an already mounted surface; inputting an arrangement position of a support pin to the displayed image; superimposing a pin arrangement image indicating the input arrangement position on the board image to create a composite image; and displaying the composite image. The composite image, a first pin arrangement image, and a second pin arrangement image are superimposed on the board image. The first pin arrangement image is generated by inputting an arrangement position in a state that the board is positioned at the first mounting work position, and the second pin arrangement image is generated on the basis of the first pin arrangement image with an assumption that the board is positioned at the second mounting work position.