A medium feeder includes: a path blocking member configured to rotate to switch between a blocking state that blocks a feed path for a medium fed out from a tray at a position of the guide member, and an open state that opens the feed path; and a switching unit that performs switching of the path blocking member, wherein the switching unit includes a rack configured to be displaced in a feeding direction in which a medium is fed from the tray to thereby perform switching of the path blocking member, and a pinion gear that drives the rack.