The present invention provides a platform step device comprising: a housing part of which the position is fixed to and disposed at a platform; a driving unit including a driving motor disposed in the housing part; a transmission unit for transmitting driving power generated from the driving unit; and a foldable step unit having a foldable step inner folding support part operated by means of the driving unit driving power transmitted through the transmission unit, so as to be operated inside the housing part, and a foldable step plate connected to at least the foldable step inner folding support part so as to rotate, around an axis of rotation, in a longitudinal direction parallel to the platform, according to the operation of the foldable step inner folding support part such that the foldable step plate can be folded, withdrawn, and accommodated.