A lumen passability checking device checks whether a capsule medical device configured to be introduced into a gastrointestinal tract of a subject is allowed to pass through the gastrointestinal tract. The device includes: a main body dissolvable by a substance in the gastrointestinal tract a first layer coating the main body, having an outer diameter substantially equivalent to an outer diameter in a minor axis of the capsule medical device, and being dissolvable by the substance in the gastrointestinal tract and a second layer coating the first layer and being dissolvable by the substance in the gastrointestinal tract. The first and second layers contain different discriminating materials. The first layer has at least two regions extending along a circumference of a cross section of the first layer, the cross section intersecting with a long axis of the device, a part of each region being thinner than other parts.
