To provide a sheet feeding device capable of feeding a sheet into an image forming device main body and coping with a thick sheet having a bulge due to a pasted part and an inlet flap like an envelope flexibly to enable smooth feeding and prevent improper conveyance.

A middle plate 312 for loading the thick sheet S like the envelope is energized in the direction for pushing it upward by a pushing-up spring 311, the envelope is also pushed upward, and an envelope at the highest position is lifted up to a level position for enabling feeding by a pick-up roller 3. Height of loading of the envelopes is regulated by a pressing member 314 (a regulation member). Since amount of bulging is absorbed by upward bending and displacing of the pressing member 314 when a bulging part occurs due to the pasted part and the flap in the envelope, the pressing member 314 is not caught in the bulge to feed sheets stably.