A new type of dynamo is found in STP-3M reversed field pinch (RFP). This dynamo generates toroidal flux uniformly along with the toroidal direction. The toroidal flux generated by this dynamo is proportional to the plasma current. It is also found that this relation is satisfied in the other RFP plasmas. The scaling of the effective inductance (proportional constant) obtained by analyzing data of typical RFP plasmas show that the effective inductance is proportional to the minor radius of the plasma. The result indicates that the force free current generates the toroidal flux. (author).