To provide a baseboard device capable of being mounted to a marginal part of an unfixed length scaffolding board of a scaffolding structure, which is positioned at a projected corner, an inner corner, or the like of a building structure.

A baseboard device is constituted of a baseboard body (7) forming a freely expandable/contractable side wall (8) and a hook mechanism (14) freely engaging the baseboard body to a support post (1). A hook is pivotally connected to a bracket so as to freely turn between a storage position (P1) along the side wall and an actuated position (P2) crossing the side wall to be projected. Movement allowable means (25) freely moving the hook between a drawing direction to and a direction separated from the bracket and a spring (26) resiliently energizing the hook in the drawing direction are included. Fixing lock means (27a) is also included. The fixing lock means faces at least the actuated position (P2), and when the hook is moved in the drawing direction by the spring, allows the hook to be received and locked in opposition to the drawing direction and irrotationally engaged, and when moving in the separated direction against the spring, unlocks the engagement to freely rotate.