There is provided a connection unit for connecting an external device to a measurement device.Connection units 600 and 700 each include a flat plate shaped connection unit main part 610, a connector terminal 651 for measurement device provided at the connection unit main part 610 and connected to a signal inputting/outputting connection port 110 or 210 corresponding to each of measurement devices 100 to 400, and a connector terminal 660 for external device provided at the connection unit main part 610 and connected to a signal inputting/outputting connection port 511 of each of external devices 510 to 540. The connection unit main part 610 is further provided with a manually operable switch.