Abstract: A platform device having utility as a ladder platform includes a frame comprising support members, two on each side, with the support members on each side being joined adjacent their upper ends and spread apart at their lower ends. There are means joining the corresponding upper and lower ends of the support members on one side with the support members on the other side. One of the support members on each side has a curved portion at the upper end thereof, which portion is formed and adapted to rest upon the rung of a ladder. The means joining the lower ends of the support members includes a lower platform which is formed and adapted to rest upon a lower adjacent ladder rung. There is a hook member pivotally attached at opposite ends thereof to the distal ends of said curved portions with the hook member being formed and adapted to be self-locking upon the upper rung.