Keyboard apparatus has a frame and a key pivotably mounted on the frame. Key guide structure includes a key-side guide member provided inside the key, and a frame-side guide member provided on the frame. The key-side guide member has at least one convexly-formed portion projecting from the inner surface of a distal end portion of the key, remote from a pivot point of the key, toward the pivot point. The frame-side guide member permits movement of the key-side guide member along a pivoting direction of the key, but limits lateral movement of the key-side guide member.