Blood purification device

A blood purification device, comprising:

• a cassette frame that, when a component of an extracorporeal circulation circuit is attached thereto, forms an integral cassette;
• and
• a cassette frame attachment part to which the cassette frame is removably attached,
• wherein the cassette frame attachment part comprises a locking portion that locks the cassette frame from the front surface side, and a pressing portion that presses the cassette frame, which is locked by the locking portion, from the back surface side,
• wherein the cassette frame comprises a locking hole through which the locking portion passes, and a pressure-receiving portion that receives pressure from the pressing portion, and
• wherein one of the pressing portion and the pressure-receiving portion comprises an inclined surface that comes into contact with the other of the pressing portion and pressure-receiving portion and converts a part of a pressing force from the pressing portion into a force in an opposite direction to a direction a locking protrusion of the locking portion faces, thereby moving the cassette frame in the opposite direction to the direction the locking protrusion faces.