| CPC F16H 19/0622 (2013.01) | 11 Claims |

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1. A spiral advancing and retreating operation device, comprising:
a first belt member; and
a second belt member,
wherein
the first and second belt members form a tubular telescopic body by spirally wrapping the first belt member and the second belt member disposed inside the first belt member around a common axis line in an overlapping manner in a state in which the first belt member and the second belt member are displaced from each other in a direction of the axis line,
the first belt member comprises a first row of engagement protrusions and a second row of engagement protrusions formed of a plurality of engagement protrusions that are disposed in a longitudinal direction of the first belt member and are convex toward the axis line,
the second belt member comprises a first row of engagement parts and a second row of engagement parts formed of a plurality of engagement parts disposed in a longitudinal direction of the second belt member,
the engagement parts are configured in such a way that the engagement protrusions can be detachably engaged therewith in a state in which the first belt member and the second belt member are spirally wrapped in the overlapping manner,
the engagement protrusions are elliptical trapezoidal protrusions, and
each engagement protrusion of the engagement protrusions has:
a bottom and a side,
a first tilt angle which is defined between the bottom and the side of the engagement protrusion in a cross section of a first plane including the direction of the axis line, and
a second tilt angle which is defined between the bottom and the side of the engagement protrusion in a cross section of a second plane including a circumferential direction of the tubular telescopic body, wherein
the first tilt angle of the engagement protrusion is larger than the second tilt angle of the engagement protrusion.
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