A sheet feeder comprising: a feed tray configured to support a sheet placed thereon; a pickup roller configured to rotate around a pickup roller axis and feed the sheet placed on the feed tray in a sheet feeding direction; a stopper movable between: a first position where the stopper is close to the pickup roller ; and a second position where the stopper is farther from the pickup roller than when the stopper is in the first position; a driving mechanism configured to move the stopper between the first position and the second position; and a set guide having a first surface facing in a particular direction such as to become farther away from a surface of the pickup roller , the set guide being rotatable around a first rotational axis along the pickup roller axis , the set guide being movable between: a third position where the first surface is positioned downstream of all the surface of the pickup roller in the particular direction; and a fourth position where the first surface is positioned upstream of at least a part of the surface of the pickup roller in the particular direction, characterized in that the first rotational axis is positioned at a middle portion of the set guide in the sheet feeding direction, wherein, in response to the stopper being placed in the first position by the driving mechanism , the stopper comes into contact with an end portion of the set guide , and the set guide is placed in the third position, and wherein, in response to the stopper being placed in the second position by the driving mechanism , the stopper is separated away from the end portion of the set guide , and the set guide is placed in the fourth position. a feed tray configured to support a sheet placed thereon; a pickup roller configured to rotate around a pickup roller axis and feed the sheet placed on the feed tray in a sheet feeding direction; a stopper movable between: a first position where the stopper is close to the pickup roller ; and a second position where the stopper is farther from the pickup roller than when the stopper is in the first position; a first position where the stopper is close to the pickup roller ; and a second position where the stopper is farther from the pickup roller than when the stopper is in the first position; a driving mechanism configured to move the stopper between the first position and the second position; and a set guide having a first surface facing in a particular direction such as to become farther away from a surface of the pickup roller , the set guide being rotatable around a first rotational axis along the pickup roller axis , the set guide being movable between: a third position where the first surface is positioned downstream of all the surface of the pickup roller in the particular direction; and a fourth position where the first surface is positioned upstream of at least a part of the surface of the pickup roller in the particular direction, a third position where the first surface is positioned downstream of all the surface of the pickup roller in the particular direction; and a fourth position where the first surface is positioned upstream of at least a part of the surface of the pickup roller in the particular direction, characterized in that the first rotational axis is positioned at a middle portion of the set guide in the sheet feeding direction, wherein, in response to the stopper being placed in the first position by the driving mechanism , the stopper comes into contact with an end portion of the set guide , and the set guide is placed in the third position, and wherein, in response to the stopper being placed in the second position by the driving mechanism , the stopper is separated away from the end portion of the set guide , and the set guide is placed in the fourth position. <EOS>