To provide a connection mechanism and an ink supply device configured to, in the case of detaching an ink cartridge from the cartridge holder of the printer body, prevent ink retained in a connection unit from scattering outside.

When the second cylindrical unit 38 of a second connection unit 11 is pushed into the first cylindrical unit 16 of a first connection unit 15 for connection, the inner peripheral protrusion 36 of a sliding member 23 of the first connection unit 15 is engaged with the outer peripheral groove 32 of a shaft member 18 and slid, and the sliding member 23 rotates, then, a moving opening 22 moves from an upper first position to a lower second position, then, the first ink path 25 of the first connection unit 15 is made to communicate with the second ink path 42 of the second connection unit 11. When the second cylindrical unit 38 is pulled out from the first cylindrical unit 16 in order to release the connection, the sliding member 23 moves along the shaft member 18 in a direction opposite to the direction, and the moving opening 22 moves from the second position to the first position, then, the first ink path 25 is shut off from the second ink path 42.