Abstract: A collapsible structure which can be readily erected and supported outside of a window against an external building wall for use by a window washer, and can be withdrawn through the opening of the window after use. The structure is in the form of a rectangular box formed of frame members pivotably fastened to each other and fitted on each side, with a diagonal strut which is pinned in position to hold the structure open, and which bears against an external wall. A pair of horizontal struts extend from the erected box across the sill of a window and are each fitted with pivotal clamp arms to grip the inside structure wall under the window sill to hold the box in position for use.