A liquid supply unit is provided with a pressure regulation valve section (36) having: a liquid discharge opening (58) capable of being connected to the upstream end of a supply flow passage (34) for supplying liquid to a liquid jet head (30); a liquid introduction opening (53) into which liquid supplied from a liquid supply source (14) is introduced, the liquid being contained in the liquid supply source (14); a pressure chamber (51), at least a part of which is formed by a flexible section (54) configured to be deformed by a change in pressure; a pressing member (56) for pressing the flexible section (54) in the direction in which the volume of the pressure chamber (51) increases; and an opening and closing valve (62) configured so as to permit the liquid to be introduced from the liquid supply source (14) into the pressure chamber (51) through the liquid introduction opening (53) in response to the deformation of the flexible section (54).