To ensure air-tightness of a rotary valve which swatches operating configuration between the push-back of an arm and the crosswise swing of a swivel base with the longitudinal and crosswise operation of the first operating handle for a backhoe.

The mutually opposite end faces of a fixed block 3 and a rotary sleeve 4 for a rotary valve 1 are inclined to form an annular storage space which is narrower as tending inward in the radial direction and seal material such as O-rings 21, 24, 28, 31, 33 are mounted in the annular storage space. The seal materials, when worn, are moved inward in the radial direction of the annular storage space to be always kept air tight. Both end faces can be reduced in machining precision. As there is not structure of compressing the seal materials with great power, no overtorque occurs when the rotary sleeve 4 is operated with angular displacement.