To provide a connection unit and a medical apparatus, capable of preventing a connection error and fraudulent connection while improving the operability for a user.

The connection unit includes: a support board 6; and a connector 7 connected to the support board 6. The support board 6 includes: a terminal 63; and a key member 64. The connector 7 includes: a terminal 71 conductive to the terminal 63 when the support board 6 is connected to the connector 7; a preventing mechanism 72 to prevent the electrical connection to the terminal 71 from outside when the support board 6 is not connected to the connector 7; and a locking mechanism 73 to retain the prevention by the preventing mechanism 72 when the support board 6 is not connected to the connector 7 and to release the prevention by the preventing mechanism 72 by engaging with the key member 64 according to the connection operation of the support board 6 to the connector 7.