A sheet feeder includes a casing, a sheet stacking portion, a sheet conveyance path, a feed roller, a separation pad, a holder, a mounting portion and a guiding member. The sheets are placed on the sheet stacking portion and fed in a predetermined direction in the sheet conveyance path. A nip portion, through which the sheet passes, is formed between the feed roller and the separation pad. The holder fixedly supports the separation pad and is mountable into and removable from the mounting portion of the casing. The guiding member guides the holder. The posture of the holder is changeable between a first posture in which a predetermined clearance is formable between the guiding member and the holder when the holder is mounted into the mounting portion and a second posture in which the holder is pressed against the guiding member when the sheet passes through the nip portion.