The invention relates to an axial bearing and to a rock drilling machine pro-vided with an axial bearing. The axial bearing (100) comprises a first piston (20) and a second piston (21). Axial contact surfaces (60, 43a) between the pistons (20, 21) are arranged in the same pressure space (28). The same pressure fluid fed to the axial bearing acts on the contact surfaces and on working pressure surfaces of the pistons.