An adhesion structure of a motor that adheres a rotor having a first linear expansion coefficient and a magnet having a second linear expansion coefficient, which differs from the first linear expansion coefficient, with an adhesive agent. The adhesion structure includes a thickness determining groove extending parallel to the axis of the rotor and arranged on the rotor in order to determine the thickness of an adhesive agent layer, which is formed from the adhesive agent. The thickness determining groove absorbs shearing stress produced by the difference between the first and second linear expansion coefficients at a surface adhered to the magnet. This effectively suppresses exfoliation of the adhesive agent layer.