Information about the affective state of a person is becoming increasingly important in human-computer interaction. This requires low-cost and unobtrusive devices to continuously measure the affective state. For this purpose, a computer mouse has been modified such that it enables measuring of mouse button pressure as the pressure applied to the mouse is highly correlated with the affective state of a person. In contrast to other studies in which mouse button pressure was analyzed, the development of the mouse was mainly driven by the requirement that the pressure sensors should not be visible from the outside that the user of the mouse does not recognize that pressure is being recorded. This can prevent intentional manipulation of the pressure applied to the mouse. Besides the button press, also the squeeze on the side of the mouse is recorded. For this purpose, a printed circuit board has been developed and integrated together with piezo and force resistive sensors into a standard computer mouse. These sensors are able to measure the force of the button press as well as the squeeze on the side of the mouse with high resolution. The mouse connects to the PC using a standard USB port. It was integrated into the xAffect software which provides an interface for data recording and visualization. A study where different arousal level were induced has shown strong interrelations between affect and mouse pressure.