To provide a connecting pin structure for a work machine preventing foreign matters such as external sediment from mixing into a pressure fluid through a bearing portion without requiring a seal for stopping the pressure fluid on the bearing portion of a pin in the connecting pin structure moved between a protrusion position where the tip of the pin is protruded from a bearing hole by the pressure fluid such as a hydraulic fluid and a retraction position where the tip of the pin is retracted into the bearing hole.

The pin is provided with a hollow section, and the hollow section is provided with a fluid pressure cylinder mechanism moving the pin to the protrusion position and the retraction position.