The present invention provides an apparatus for manufacturing spout-equipped bags to prevent inadequate gripping by grippers by making left and right gripping margins on a bag for the grippers essentially equal even during corner spout attachment in a type of apparatus for manufacturing spout-equipped bags in which the opposite edges of a bag are gripped by a pair of left and right grippers, the bag is conveyed along a predetermined conveying path, and a spout is attached to the mouth of the bag in the conveyance process, and in which both corner spout attachment and center spout attachment are both performed. Unloading suction members (13) adheres by suction to a bag in a horizontal orientation in a bag conveying device hopper type empty bag supplying device (12) and takes out the bag (11); and then bag suction members (36) adheres to the bag (11) and changes the bag into a vertical orientation, the bag is then rotated through a predetermined angle, making the bag mouth horizontal. A transfer chuck (52) grips the bag (11) and conveys it towards grippers (3, 3), and the bag is displaced a predetermined distance horizontally and supplied to the grippers. The horizontal displacement distance of the transfer chuck (52) is set in advance such that gripping margins on the bag (11) for the grippers (3, 3) are made substantially equal on the left and right of the bag (11).