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 mode determination unit configured to determine an operation mode which is selected from a plurality of operation modes including a normal mode and a high-speed mode in which an operation is executed at a higher speed than the normal mode; a control unit configured to select and control to execute one of the first candidate decision processing and the second candidate decision processing for each of a plurality of feature points in accordance with the operation mode determined by the mode determination unit; and a correction unit configured to correct the position candidates of the plurality of feature points obtained by the first candidate decision processing or the second candidate decision processing based on a layout relationship among the plurality of feature points in any operation mode, wherein in the high-speed mode, said control unit selects and controls to execute the second candidate decision processing for more feature points than in the normal mode.