The present invention relates to a circular stapler used for an operation of cutting off and suturing a jejunum, where a structure of the circular stapler is improved to facilitate manipulation thereof and to enhance the potential for success of the operation. The circular stapler comprises: a detachable anvil; a head section coupled to the detachable anvil and having a head section cover; and a cylindrical body which extends longs and of which the top end is coupled to the head section, and a recessed portion is formed in a side surface of the cylindrical body positioned under the head section cover. According to the circular stapler, it is possible to considerably reduce the potential for constricting the small intestine, to reduce the bleeding, which may be generated due to the stapling in a state where the tension is applied, and to reduce a risk that the small intestine is caught by the head section of the circular stapler during the suturing operation.