The object of the present invention is to provide a laminated film made of polylactic acids which is not prone to delamination while having excellent piezoelectric properties and a manufacturing method thereof. That is, the present invention is obtained by the stretched laminated film manufactured by a co-extrusion process for use in piezoelectric polymer materials, containing a layer (A) which has poly-L-lactic acid as the primary component and contains an impact modifier in the range of 0.1 to 10 mass % and a layer (B) which has poly-D-lactic acid as the primary component and contains an impact modifier in the range of 0.1 to 10 mass %.