A liquid supply apparatus configured to supply a liquid to a printing unit, comprising a tray holder configured to hold a tray on which a flexible retaining container configured to retain a liquid is placed, the tray holder allowing insertion of the tray in a first direction, wherein the retaining container has a foldable gusset portion, and the tray holder is provided with a folding unit configured to fold the gusset portion in a state in which the tray is held by the tray holder.