In a focal plane shutter for a single lens reflex camera having, on the side of the shutter aperture, two blade groups each consisting of a plurality of separate blades adapted to operate sequentially in exposure operation, a shutter blade device includes said two blade groups having at least some of blades formed of thin synthetic resin plates. A shielding member is provided between a reflex mirror and said blade groups and adapted to retract from an aperture shielding position during the exposure operation of said two blade groups and return to an aperture shielding position before and after the exposure operation.