A rotor magnet installation structure includes: a first shaft including a shrinkage-fit portion in which an accommodation space is formed; at least one magnet inserted in the accommodation space, an installation outer diameter of the magnet being greater than an inner diameter of the accommodation space before the magnet is inserted in the accommodation space; and a second shaft comprising a connection portion inserted in the accommodation space, an outer diameter of the connection portion being greater than the inner diameter of the accommodation space before the connection portion is inserted in the accommodation space.