As a respiration synchronized-type gas supplying apparatus which has a function for setting the flow rate during continuous supply and at the same time can be miniaturized by simplifying the structure, the present invention provides an oxygen supplying apparatus comprising an oxygen generating means, an oxygen supplying means for supplying the oxygen generated by the oxygen supplying means to a user and an automatic closing valve placed on the oxygen-supplying passage, wherein the oxygen supplying apparatus is provided with the following: a respiration sensor which detects the respiration of a user; a supply method setting means which selects the supply in a continuous flow or the supply in synchronism with the respiration of the user; a flow rate setting means for a supply flow rate; and a controlling means which controls the aperture of the closing valve corresponding to the set value of the flow rate setting means by receiving a supply method setting signal of the continuous flow, or opens the automatic closing valve on the inhalation starting point based on the respiration signal of the respiration sensor by receiving a supply method setting signal of the synchronous flow and at the same time controls the open time of the automatic closing valve corresponding to the flow rate set value.