A water absorption property of a concrete surface of an actual structure is measured in situ for clarification and evaluation of causative factors and so forth related to densification of surface layer concrete. An apparatus for a water absorption test has a position-fixing device, a detecting device and a measuring device. A device for water absorption test having vent means is positionally fixed on the concrete surface by the position-fixing device, with use of negative pressure or a mechanical connection. The detecting device detects an amount of water held in a chamber, and results detected by the detecting device are input into the measuring device. A water absorption rate is measured by the detecting device and the measuring device. On the basis of the water absorption rate measured at predetermined elapsed time, identification or comparison of causative or evaluative factors related to densification of the surface layer concrete is carried out.