An automatic analyzer, comprising: a sample probe configured to suck a specimen and discharge the specimen into a reaction vessel; a reagent probe configured to suck a reagent and discharge the reagent into the reaction vessel; a photometer configured to analyze a mixture of the specimen and the reagent in the reaction vessel; a reagent disk configured to hold a reagent bottle storing the reagent; a needle configured to form a cut in a lid of the reagent bottle; a lid opening mechanism (40, 104) configured to drive the needle; and a controller configured to control the lid opening mechanism, characterised in that: the needle comprises: a piercing portion including a plurality of blades for forming the cut in the lid of the bottle and a cylindrical expansion portion configured to push and open the cut, the plurality of blades are disposed at vertices of a regular polygon as viewed from a distal end of the piercing portion, the cylindrical expansion portion has a diameter which is smaller than a maximum diameter of a circumscribed circle of the plurality of blades of the piercing portion but is equal to or larger than a maximum diameter of the reagent probe within a range within which the reagent probe is inserted into the reagent bottle before the reagent probe sucks the reagent, and the controller is configured to control the lid opening mechanism so that the needle is inserted to the expansion portion to push and open the cut after the cut has been formed in the lid of the bottle by the piercing portion. a sample probe configured to suck a specimen and discharge the specimen into a reaction vessel; a reagent probe configured to suck a reagent and discharge the reagent into the reaction vessel; a photometer configured to analyze a mixture of the specimen and the reagent in the reaction vessel; a reagent disk configured to hold a reagent bottle storing the reagent; a needle configured to form a cut in a lid of the reagent bottle; a lid opening mechanism (40, 104) configured to drive the needle; and a controller configured to control the lid opening mechanism, characterised in that: the needle comprises: a piercing portion including a plurality of blades for forming the cut in the lid of the bottle and a cylindrical expansion portion configured to push and open the cut, the plurality of blades are disposed at vertices of a regular polygon as viewed from a distal end of the piercing portion, the cylindrical expansion portion has a diameter which is smaller than a maximum diameter of a circumscribed circle of the plurality of blades of the piercing portion but is equal to or larger than a maximum diameter of the reagent probe within a range within which the reagent probe is inserted into the reagent bottle before the reagent probe sucks the reagent, and the controller is configured to control the lid opening mechanism so that the needle is inserted to the expansion portion to push and open the cut after the cut has been formed in the lid of the bottle by the piercing portion. the needle comprises: a piercing portion including a plurality of blades for forming the cut in the lid of the bottle and a cylindrical expansion portion configured to push and open the cut, the plurality of blades are disposed at vertices of a regular polygon as viewed from a distal end of the piercing portion, the cylindrical expansion portion has a diameter which is smaller than a maximum diameter of a circumscribed circle of the plurality of blades of the piercing portion but is equal to or larger than a maximum diameter of the reagent probe within a range within which the reagent probe is inserted into the reagent bottle before the reagent probe sucks the reagent, and the controller is configured to control the lid opening mechanism so that the needle is inserted to the expansion portion to push and open the cut after the cut has been formed in the lid of the bottle by the piercing portion.