The present invention provides an elongation measuring apparatus, an elongation measurement system and a non-transitory medium recording a computer program, which enable measurement of an elongation of a chain without presetting a distance between rollers before use. Based on an image of three or more pins, two adjacent inter-pin distances are each calculated. As a result of a comparison between the two calculated inter-pin distances, the longer distance is determined as a pitch of an inner link and the shorter distance is determined as a pitch of an outer link. The outer link is not elongated while only the inner link is elongated, and therefore, a ratio of a difference between both of the pitches to the pitch of the outer link is determined as an elongation of a chain.