A thread monitoring mechanism for a thread processing location with a swivel lever which is mounted on a swivel axis and on which a thread guidance roller overrun by the thread that is to be monitored is mounted and which is elastically supported by a supporting member adjustable in accordance with a predetermined thread tension, in which respect the swivel lever has a switching member for interrupting the thread travel and/or for switching-off the thread processing location as soon as the actual thread tension deviates by a specific amount from a predetermined thread tension value, is characterized in that the suporting member is pneumatically supported, in which respect serving for supporting the swivel lever are preferably two supporting members which are supported pneumatically by membranes which have effective membrane surfaces of different sizes.