An automated analyzer includes a container installation portion in which a container, such as a reagent container, has a protrusion and an openable and closable lid. A lid opening and closing mechanism opens and closes the lid and includes an arm portion having an arm and a horizontal driving portion which moves the arm in a first horizontal direction. The arm includes a protrusion contacting portion that includes a first surface having an angle greater than 0 degrees and less than 90 degrees when the horizontal surface is set as 0 degrees. The lid opening and closing mechanism portion opens the lid by moving the arm in the first horizontal direction, contacting the lid protrusion on the first surface of the protrusion contacting portion, and then moving the lid protrusion along a shape of the first surface in a vertical direction, until the lid is opened.