Abstract: The present invention relates to a pair of meshed involute gears one of which has work teeth, their tooth-tip circle is larger than that of the said gear, the other has the grooves engaged with the said working teeth. The working teeth and the grooves have the same characters of equal periphery of meshing and rotating as the said involute gears. This composite construction of the gear named "the meshing type rotors" can be used in making internal combustion engine, fluid (liquid or gasous) pump and motor, vacuum pump, conditioner/refrigerator/compressor and hydraulic variator.