A spindle device comprising: a rotary shaft (12, 12'); front and rear bearings (50, 60) each configured to rotatably support the rotary shaft with respect to a housing; and a motor including a rotor fitted onto the rotary shaft (12, 12') at a location between the front and rear bearings (50, 60), and a stator disposed around the rotor, wherein the rotary shaft (12, 12') comprises: a first cylindrical member made of a metal material, and a second cylindrical member having an outer peripheral surface on which the rotor is fitted, the second cylindrical member being made of a material having high specific elastic modulus and low linear expansion coefficient relative to the metal material of the first cylindrical member. the second cylindrical member being disposed on an outer peripheral surface of the first cylindrical member, characterized in that the first cylindrical member is formed to be longer than the second cylindrical member, and has a small-diameter portion (71 a) in which the second cylindrical member is disposed, and a large diameter portion (71 c) having a male threaded portion (71 b) to which a nut regulating an axial position of the inner rings of the front bearings is fastened, and an end portion, on a side opposite to a tool side, of the small-diameter portion (71 a) extending from the second cylindrical member is provided with a male screwed portion (71 d) to which another nut for restraining the axial position of the inner rings of the rear bearings is fastened. a rotary shaft (12, 12'); front and rear bearings (50, 60) each configured to rotatably support the rotary shaft with respect to a housing; and a motor including a rotor fitted onto the rotary shaft (12, 12') at a location between the front and rear bearings (50, 60), and a stator disposed around the rotor, wherein the rotary shaft (12, 12') comprises: a first cylindrical member made of a metal material, and a second cylindrical member having an outer peripheral surface on which the rotor is fitted, the second cylindrical member being made of a material having high specific elastic modulus and low linear expansion coefficient relative to the metal material of the first cylindrical member. the second cylindrical member being disposed on an outer peripheral surface of the first cylindrical member, characterized in that the first cylindrical member is formed to be longer than the second cylindrical member, and has a small-diameter portion (71 a) in which the second cylindrical member is disposed, and a large diameter portion (71 c) having a male threaded portion (71 b) to which a nut regulating an axial position of the inner rings of the front bearings is fastened, and an end portion, on a side opposite to a tool side, of the small-diameter portion (71 a) extending from the second cylindrical member is provided with a male screwed portion (71 d) to which another nut for restraining the axial position of the inner rings of the rear bearings is fastened. a first cylindrical member made of a metal material, and a second cylindrical member having an outer peripheral surface on which the rotor is fitted, the second cylindrical member being made of a material having high specific elastic modulus and low linear expansion coefficient relative to the metal material of the first cylindrical member. the second cylindrical member being disposed on an outer peripheral surface of the first cylindrical member, characterized in that the first cylindrical member is formed to be longer than the second cylindrical member, and has a small-diameter portion (71 a) in which the second cylindrical member is disposed, and a large diameter portion (71 c) having a male threaded portion (71 b) to which a nut regulating an axial position of the inner rings of the front bearings is fastened, and an end portion, on a side opposite to a tool side, of the small-diameter portion (71 a) extending from the second cylindrical member is provided with a male screwed portion (71 d) to which another nut for restraining the axial position of the inner rings of the rear bearings is fastened.