Recently, the microrobot powered by biological muscle actuators was proposed. The cell based actuator utilizes glucose as a power source and thus can apply to the application of a human body or blood vessels. For the structural design of the cell based micro-robot, the contractile force of the muscle powered by cardiac myocytes should be measured. In addition, the contractile force measurement can be used in the static or dynamic simulations of the micro-robot. In this paper, the contractile force measurement system, which is composed of a micro-manipulator, a force transducer, a signal processor and an inverted microscope is proposed. By using the measuring system, the contractile force for both control and micro-patterned cardiac myocytes are measured. From the experimental results, we estimated that the contractile force of cardiac myocytes is about 20-40 N when it is compared between the control cell and the cell on micro pattern.