An angle of rotation detection device comprising: an electrical angle detector (12, 14) having an electrical angle corresponding to one period of an output signal set smaller than a mechanical angle of 360° and adapted to provide a two-phase encoder signal corresponding to the electrical angle of a rotor, and a two-phase encoder counter (41; 41A; 41B) adapted to count said two-phase encoder signal to output a digital value corresponding to said electrical angle corresponding to said electrical angle of 360° as a maximum counting value, characterized in that the angle of rotation detection device further comprises: a multiplication factor detector (42; 42A; 42B) adapted to detect which position of the mechanical angle an angle indicated by a signal output from said electrical angle detector (12, 14) corresponds to, based on a change of a count value of said two-phase encoder counter (41; 41A; 41B), wherein said multiplication factor detector (42; 42A; 42B) adapted to generate, based on a change of a count value of said two-phase encoder counter (41; 41A; 41B), an extended count value for extending a number of bits of said two-phase encoder counter (41; 41A; 41B) which can express at most a value corresponding to the electrical angle of 360° to the number of bits which can express a value corresponding to the mechanical angle of 360°, and to output said extended count value as a value showing which position of the mechanical angle the electrical angle indicated by the signal output from said electrical angle detector (12, 14) corresponds to, and an upper limit of said extended count value corresponding to a multiplication factor of said electrical angle detector (12, 14). an electrical angle detector (12, 14) having an electrical angle corresponding to one period of an output signal set smaller than a mechanical angle of 360° and adapted to provide a two-phase encoder signal corresponding to the electrical angle of a rotor, and a two-phase encoder counter (41; 41A; 41B) adapted to count said two-phase encoder signal to output a digital value corresponding to said electrical angle corresponding to said electrical angle of 360° as a maximum counting value, characterized in that the angle of rotation detection device further comprises: a multiplication factor detector (42; 42A; 42B) adapted to detect which position of the mechanical angle an angle indicated by a signal output from said electrical angle detector (12, 14) corresponds to, based on a change of a count value of said two-phase encoder counter (41; 41A; 41B), wherein said multiplication factor detector (42; 42A; 42B) adapted to generate, based on a change of a count value of said two-phase encoder counter (41; 41A; 41B), an extended count value for extending a number of bits of said two-phase encoder counter (41; 41A; 41B) which can express at most a value corresponding to the electrical angle of 360° to the number of bits which can express a value corresponding to the mechanical angle of 360°, and to output said extended count value as a value showing which position of the mechanical angle the electrical angle indicated by the signal output from said electrical angle detector (12, 14) corresponds to, and an upper limit of said extended count value corresponding to a multiplication factor of said electrical angle detector (12, 14). a multiplication factor detector (42; 42A; 42B) adapted to detect which position of the mechanical angle an angle indicated by a signal output from said electrical angle detector (12, 14) corresponds to, based on a change of a count value of said two-phase encoder counter (41; 41A; 41B), wherein said multiplication factor detector (42; 42A; 42B) adapted to generate, based on a change of a count value of said two-phase encoder counter (41; 41A; 41B), an extended count value for extending a number of bits of said two-phase encoder counter (41; 41A; 41B) which can express at most a value corresponding to the electrical angle of 360° to the number of bits which can express a value corresponding to the mechanical angle of 360°, and to output said extended count value as a value showing which position of the mechanical angle the electrical angle indicated by the signal output from said electrical angle detector (12, 14) corresponds to, and an upper limit of said extended count value corresponding to a multiplication factor of said electrical angle detector (12, 14).