As vision-based tactile sensor consists of no electronic elements such as resistors and capacitors, it is easy to be small size and free of the influence of the environment. A vision-based tactile sensor is made of a camera and a transparent elastic body with markers inside. When a force is applied to the sensor, the elastic body deforms and the markers move. The camera captures the movements of the markers. Then the force applied on the sensor is calculated by elastic theory and the movements of the markers. The signal processing circuit is a circuit with a small size FPGA EP4CGX30 served as data process unit and can catch pictures with a high speed, identify the location of markers and calculate the movements of markers and the force applied on the sensor. The size of the circuit is small enough to be put into the second part of the mechanical finger.