A lubrication structure for a working machine is provided that can evenly supply lubricant to a sliding contact surface between an eccentric cam and a crank member regardless of lubricant used and the use environment. A driven gear 12 that engages with a driving gear 11 connected to a driving source and rotates, is accommodated in a chamber 3 in a case 3. An eccentric cam 13 is provided on a surface 12a of the driven gear 12, and connected to a coupling pin 5a in a blade 5 through a crank member 16. A fitting ring part 16b is provided in one end of the crank member 16, and the eccentric cam 13 is inserted into the fitting ring part 16b so as to rotate relative to the fitting ring part 16b. An annular groove 30 is formed on the inner surface of the fitting ring part 16b which faces the outer surface of the eccentric cam 13. The annular groove 30 communicates with a first chamber 33a via a first lubricating passageway 31 and also communicates with a second chamber 33b via a second lubricating passageway 32. The pressure in the first chamber 33a is higher than that is the second chamber 33b.
