A portable screen assembly includes: a casing having an opening extending in a longitudinal direction on the upper surface thereof, and formed by a pair of separable case members that extend in the longitudinal direction; a spring-biased roll rotatably mounted in the casing; a screen wound around the spring-biased roll in a storage position and extended from the opening in use; a top bar fixed to one end of the screen which is used as a cover body to close the opening in the storage position; and an extendable column having one end erectably pivoted from a center part of a side face of the casing to hold the screen in a stretched state.