According to an example of the invention, a test tube holder includes a holder body including a cylindrical wall defining a cylindrical hollow portion, at least three guide grooves in the cylindrical wall and open on the inner peripheral side and upper end surface side, cam grooves which face the guide grooves and inclined obliquely upward, a plurality of holder members for test tube attachment which are fitted individually in the guide grooves of the holder body so as to be movable vertically and radially, cam pins which engage with the cam grooves so as to guide the holder member vertically and radially, and an urging spring which elastically urges the holder member to be pushed up so that the holder member is pressed upward and toward the inner periphery of the cylindrical wall.