A method for inspecting a pillar-shaped honeycomb structure including the steps of: imaging a pattern of transmitted light from the second end face according to arrangement of the plugged portions of first cells and second cells, with a camera via a light diffusing film placed parallel to a second end face of the pillar-shaped honeycomb structure in a non-contact state with the second end face, which pattern is obtained by irradiating a first end face with light; and detecting a defective plugged portion(s) of the second cells based on an image of the pattern of transmitted light imaged with the camera.