A medium loading device includes a side end aligning member which is positioned at a standby position when a medium is ejected; and a control section. When a value based on first information relating to recording density of a medium to be ejected this time and at least one medium among the media ejected previously is equal to or greater than a threshold value, the control section specifies a first position, which overlaps the medium to be ejected this time, as the standby position, and when the value based on the first information is less than the threshold value, the control section specifies a second position, which does not overlap the medium to be ejected this time, as the standby position, and the control section adjusts the threshold value based on second information relating to at least one medium among the media recorded before the ejection at this time.