1. A feature point positioning apparatus which positions a plurality of feature points for a predetermined pattern in image data, comprising: a first candidate decision unit configured to execute first candidate decision processing to decide position candidates of the feature points; a second candidate decision unit configured to execute second candidate decision processing having a higher processing speed than the first candidate decision processing to decide position candidates of the feature points; a control unit configured to control said first candidate decision unit and said second candidate decision unit to selectively execute the first candidate decision processing and the second candidate decision processing for the respective feature points in accordance with an operation mode; and a correction unit configured to correct the position candidates of the plurality of feature points obtained by the first candidate decision processing and the second candidate decision processing based on a layout relationship among the plurality of feature points, wherein when the operation mode is a high-speed mode in which an operation is executed at a higher speed than a normal mode, said control unit controls to execute the second candidate decision processing for more feature points than in the normal mode.