An autofocus support method according to an embodiment supports autofocus for a semiconductor device having a substrate and a device pattern formed on one main surface side of the substrate. The method includes: a step of acquiring a first image focused on the substrate; a step of acquiring a spatial frequency image from the first image by Fourier transform and generating mask data for masking linear patterns in the same direction on the substrate based on the spatial frequency image; a step of performing filtering on a plurality of second images, which are captured by using an imaging device while changing the focal position of the imaging device on the other main surface side of the substrate, by using the mask data; and a step of focusing the imaging device on the device pattern based on the second image after filtering.