A sheet supply device that feeds a sheet placed on a sheet supply tray comprising: a delivery roller that can be freely elevated/lowered and contacts a topmost surface of a sheet bundle on the sheet supply tray to deliver the sheet; an elevating tray that can be freely elevated/lowered and supports a leading end side of the sheet bundle placed on the sheet supply tray; and a first drive section (M1, 43) that elevates/lowers the elevating tray; a second drive section (M2, 45) that elevates/lowers the delivery roller; a controller that controls drive of the first and second drive sections (M1, 43; M2, 45), characterized by further comprising: a top surface detection section that detects a position of a topmost surface of the sheet bundle on the sheet supply tray, wherein when the top surface position detection section detects a state where the topmost surface of the sheet bundle on the sheet supply tray is situated below a predetermined position, the controller controls the first and second drive sections (M1, 43; M2, 45) so as to elevate the elevating tray until the topmost surface of the sheet bundle on the sheet supply tray reaches the delivery position and thereafter lower the delivery roller to a position where it contacts the topmost surface of the sheet bundle, and when the top surface position detection section detects a state where the topmost surface of the sheet bundle on the sheet supply tray is situated at a predetermined position or above the predetermined position, the controller controls the first and second drive sections (M1, 43; M2, 45) so as to lower the delivery roller to a position where it contacts the topmost surface of the sheet bundle with a position of the elevating tray maintained. a delivery roller that can be freely elevated/lowered and contacts a topmost surface of a sheet bundle on the sheet supply tray to deliver the sheet; an elevating tray that can be freely elevated/lowered and supports a leading end side of the sheet bundle placed on the sheet supply tray; and a first drive section (M1, 43) that elevates/lowers the elevating tray; a second drive section (M2, 45) that elevates/lowers the delivery roller; a controller that controls drive of the first and second drive sections (M1, 43; M2, 45), characterized by further comprising: a top surface detection section that detects a position of a topmost surface of the sheet bundle on the sheet supply tray, wherein when the top surface position detection section detects a state where the topmost surface of the sheet bundle on the sheet supply tray is situated below a predetermined position, the controller controls the first and second drive sections (M1, 43; M2, 45) so as to elevate the elevating tray until the topmost surface of the sheet bundle on the sheet supply tray reaches the delivery position and thereafter lower the delivery roller to a position where it contacts the topmost surface of the sheet bundle, and when the top surface position detection section detects a state where the topmost surface of the sheet bundle on the sheet supply tray is situated at a predetermined position or above the predetermined position, the controller controls the first and second drive sections (M1, 43; M2, 45) so as to lower the delivery roller to a position where it contacts the topmost surface of the sheet bundle with a position of the elevating tray maintained. a top surface detection section that detects a position of a topmost surface of the sheet bundle on the sheet supply tray, wherein when the top surface position detection section detects a state where the topmost surface of the sheet bundle on the sheet supply tray is situated below a predetermined position, the controller controls the first and second drive sections (M1, 43; M2, 45) so as to elevate the elevating tray until the topmost surface of the sheet bundle on the sheet supply tray reaches the delivery position and thereafter lower the delivery roller to a position where it contacts the topmost surface of the sheet bundle, and when the top surface position detection section detects a state where the topmost surface of the sheet bundle on the sheet supply tray is situated at a predetermined position or above the predetermined position, the controller controls the first and second drive sections (M1, 43; M2, 45) so as to lower the delivery roller to a position where it contacts the topmost surface of the sheet bundle with a position of the elevating tray maintained.