Length measurement device

A length measurement device comprising:

• a placement table having a placement surface including a placement region on which an object to be measured is placed;
• first cameras provided to respectively correspond to target points which are both ends of a length measurement target portion of the object to be measured that is placed on the placement region and configured to capture an image of an imaging range, wherein the imaging range is disposed to include the corresponding target points when the object to be measured is placed on the placement region;
• first marks respectively provided in a plurality of imaging ranges outside the placement region on the placement surface;
• a memory configured to store positions of the plurality of first marks on the placement surface as first mark reference positions in advance;
• a processor configured to perform an image position acquiring process of acquiring a target image position which is a position of each of the target points in each of captured images and a first mark image position which is a position of each of the first marks in each of the captured images on the basis of the captured images captured by each of the first cameras when the object to be measured is placed on the placement region, obtain a position of each of the target points on the placement surface on the basis of the target image position and the first mark image position corresponding to each of the plurality of captured images and each of the first mark reference positions which is a position of each of the first marks on the placement surface, and obtain a length of the length measurement target portion on the basis of the position of each of the target points obtained by the processor.