To prevent, in a medical device that includes a tip-side device to be brought into contact with or inserted into an object to be observed and a root end-side device connected to the tip-side device, the leakage of radiation noise generated in the root end-side device to the outside and the entry of disturbance noise into the root end-side device. A connection structure includes: a plug provided at a root end of the tip-side device and a receptacle provided in the root end-side device and configured to hold the plug by insertion. At least one of the plug and the receptacle contains an electrically non-conductive magnetic material in a portion crossing an opening formed in the outer casing in a state where the plug is inserted in the receptacle.
