Abstract: An apparatus for measuring the surface hardness of building materials, having a housing comprising a test hammer, a driving spring and an impact pin, said test hammer being moveable by means of said driving spring along a path in said housing to be brought to impact against said impact pin, which for measurement is placed on the surface to be measured, and further having measuring device for measuring a rebound height of said test hammer wherein said test hammer is provided with an optical pattern extending over at least part of its length and wherein said measuring device comprises an optical detection unit arranged adjacently to said path of the test hammer and provided for detecting said optical pattern of the test hammer, and wherein said measuring device further comprises an evaluation circuit connected to said optical detection unit to determine the maximum height of the rebounding hammer at the upper end of its path after impact.