PROBLEM TO BE SOLVED: To provide a connection structure capable of improving the flexibility of freedom of adjusting the positional relationship and attitude of a sub device supported by a medical main device, and sufficiently securing support force to the sub device.SOLUTION: A connection structure includes: coupling parts 8 and 15 with a cylinder circumferential surface respectively provided on a medical main device 1 and a sub device 2 and a connection member 3 having, at both ends, first and second fitting parts 9 and 10 to be respectively fitted to the cylinder circumferential surfaces of the coupling parts. The connection member is configured so as to be turnable to the main device and the sub device through the fitting of the first and second fitting parts, and to displaceably support the sub device by the main device through the connection member. The coupling part of the sub device is constituted of an inner side fitting part 18, and the second fitting part is constituted of an outer side fitting part 10 fitted to the outer side of the inner side fitting part.
