To make amplitude of linear reciprocating member continuously changeable without requiring troublesome disassembling and assembling work and troublesome part replacement, in a rotary-linear motion converting mechanism.

The rotary-linear motion converting mechanism 54 includes a rotatable cylindrical cam 66 provided with a cam groove 118, a contact element 110 for guiding along the cam groove 118, an oscillation rod 112 for supporting the contact element 110, a gear shift rod 114, a rod supporting bracket 116, and a linear motion bracket 68. The gear shift rod 114 is movably/rotatably supported by the oscillation rod 112 in the longitudinal direction and can move only in a direction orthogonal to a direction in parallel with the axial direction of the cylindrical cam 66. The linear motion bracket 68 is rotatably supported by the rod supporting bracket 116 which is supported by the oscillation rod 112 to be movable in the longitudinal direction and can reciprocate only in a linear direction in parallel with the axial direction of the cylindrical cam 66.

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