We investigate the measurement of real contact area, denoted by Ar, between various floor materials and rubber. Observation of Ar plays an important role for better understanding of frictional force. The Ar between them, however, has yet to be observed over regions wider than what an optical microscope can cover. Current optical microscopy techniques are limited by the measurement time required to observe the whole apparent contact area. Further, it is difficult to reproduce actual contact situations between the rubber and the floor materials because at least one of the contacting specimens must be transparent. Usually, glass plates much harder than rubber are used as counter specimens. In this study, we observed the Ar between a transparent silicone rubber and the various floor materials by using a laser microscope with a wide field of view, allowing us to observe the whole apparent contact area of 9 mm × 7 mm for a very short time. By using transparent rubber, we were able to reproduce the actual contact situations of the rubber-floor specimens, which is impossible with glass plates. The measurement of Ar when the apparent contact area was too small suffered from large fluctuations in measurement values due to waviness of the floor specimen. We investigated the apparent contact area required to accurately understand the relationship between frictional force and Ar and clarified the influence of waviness of the floor materials on the distribution of Ar. •We measure real contact area, Ar, between various floor materials and rubber.•We use an ultra-transparent silicone rubber instead of a glass plate.•Measurement values of Ar in small regions show large fluctuation.•Wide field of view microscope leads to less variation in measurement values of Ar.•Effect of grooves in floor specimen on the distribution of Ar is clearly demonstrated.