Protective film for a polarizer, a polarizing plate comprising the same, and a display device with the polarizing plate

A protective film for a polarizer, which

• comprises polyethylene terephthalate (PET),
• satisfies the in-plane phase difference and phase difference in the thickness direction conditions of (1) and (2) at a wavelength of 550 nm:
• (1) in-plane phase difference (Ro)≦350 nm
• (2) 16,000 nm≧phase difference in thickness direction (Rth)≧6,000 nm,
• experiences change in the phase difference in the thickness direction with respect to the width change within the effective width (|ΔRth|/|Δx|) of less than 1.5 nm/mm, and
• experiences variation in the phase difference in the thickness direction within the effective width (Rth,max−Rth,min) of 1,500 nm/m or less.