PURPOSE: To provide a hydraulic actuation mechanism which can attain miniaturization and weight reduction of a portable shearing machine and the portable shearing machine.

CONSTITUTION: A crankshaft 35 integratedly connected to the front edge of a rotary drive shaft 34 is provided. The crankshaft 35 is provided with two eccentric cam parts 35A, 35B in line, respective eccentric quantities are equal to each other, and they are positioned at angular intervals of 180 degrees. Needle bearings 38 arranged on the outer circumference of the respective cam parts are brought in slidable contact with respective plungers 101 of pump units 100A, 100B, and the respective plungers are alternately elevatably moved at correct phase interval of 180 degrees. Hence, in the pump part, at every half rotation of the rotary drive shaft 34, the first pump unit and the second pump unit continue suction of hydraulic oil in a oil reservoir and force feed of the oil to the oil pressure chamber 52 of a cylinder device 5.