This paper proposes a method of map merging using cycle consistency check and spanning tree selection by RANSAC. Key issues in map merging are the transformation of the coordinate frame of each submap to a global coordinate frame and the rejection of outliers (false arcs) in a pose graph. The proposed method reduces outliers using cycle consistency constraints. To cope with the exponential increase of cycles, cycle consistency check is applied iteratively with a limited number of chordless cycles. Then, spanning trees having only inlier arcs are selected by RANSAC to find the transformation of each submap to a global coordinate frame. Experiments using public datasets show that the proposed method successfully obtained good spanning trees at high outlier ratio.