A shaking device comprising: a driving shaft which is driven by an engine and has a pinion ; a crankshaft unit driven by the pinion of the driving shaft ; a connecting rod ; and a pole having a contacting part at a forward end of the pole , the pole being reciprocated between a forward position and a backward position along a reciprocating axis (A) by the crankshaft unit via the connecting rod ; wherein the crankshaft unit includes a crankshaft portion engaging the connecting rod , and a reverse-rotation portion ; wherein the crankshaft portion includes a first flywheel driven by the pinion to rotate in a first rotational direction (R1), and at least one normal-rotation counterweight ; wherein the reverse-rotation portion includes a second flywheel driven by the pinion to rotate in a second rotational direction (R2) opposed to the first rotational direction (R1), and at least one reverse-rotation counterweight ; wherein the first flywheel is disposed on a first side of the reciprocating axis (A), while the second flywheel and the at least one reverse-rotation counterweight are disposed on a second side of the reciprocating axis (A) opposite to the first side; and wherein the at least one normal-rotation counterweights and the at least one reverse-rotation counterweight are arranged so as to be positioned at a backward position when the pole is in the forward position and so as to be positioned at a forward position when the pole is in the backward position; characterized in that the at least one normal-rotation counterweight includes at least one first normal-rotation counterweight arranged on the first side of the reciprocating axis (A) and at least one second normal-rotation counterweight arranged on the second side of the reciprocating axis (A), and the at least one reverse-rotation counterweight is arranged between the at least one first normal-rotation counterweight and the at least one second normal-rotation counterweight . a driving shaft which is driven by an engine and has a pinion ; a crankshaft unit driven by the pinion of the driving shaft ; a connecting rod ; and a pole having a contacting part at a forward end of the pole , the pole being reciprocated between a forward position and a backward position along a reciprocating axis (A) by the crankshaft unit via the connecting rod ; wherein the crankshaft unit includes a crankshaft portion engaging the connecting rod , and a reverse-rotation portion ; wherein the crankshaft portion includes a first flywheel driven by the pinion to rotate in a first rotational direction (R1), and at least one normal-rotation counterweight ; wherein the reverse-rotation portion includes a second flywheel driven by the pinion to rotate in a second rotational direction (R2) opposed to the first rotational direction (R1), and at least one reverse-rotation counterweight ; wherein the first flywheel is disposed on a first side of the reciprocating axis (A), while the second flywheel and the at least one reverse-rotation counterweight are disposed on a second side of the reciprocating axis (A) opposite to the first side; and wherein the at least one normal-rotation counterweights and the at least one reverse-rotation counterweight are arranged so as to be positioned at a backward position when the pole is in the forward position and so as to be positioned at a forward position when the pole is in the backward position; characterized in that the at least one normal-rotation counterweight includes at least one first normal-rotation counterweight arranged on the first side of the reciprocating axis (A) and at least one second normal-rotation counterweight arranged on the second side of the reciprocating axis (A), and the at least one reverse-rotation counterweight is arranged between the at least one first normal-rotation counterweight and the at least one second normal-rotation counterweight . <EOS>