PURPOSE: To obtain a friction tester capable of accurately testing and measuring the friction characteristics of a test piece generating friction force in the tangential direction of a contact surface in various atmospheres.

CONSTITUTION: Load is applied to the test pieces 14,15 in a measuring chamber 3 by a load applying mechanism 5 and the friction force in a tangential direction generated by the rotation of the drive shaft 25 in a bearing chamber 4 is measured by a friction force measuring mechanism. Since the measuring chamber 3 and the bearing chamber 4 are separated so that the gap both chambers is hermetically closed by an oil seal 22, the measuring chamber 3 can be held to various atmospheres such as vacuum or the like. Since both chambers 3,4 can be controlled to the same pressure by a bypass mechanism 9, nol leak is generated from the oil seal 22 even under a high pressure atmosphere and a friction test can be performed.