In a focus detection device for a camera, a plurality of distance sensors each for detecting a distance to an object in a plurality of areas of a photographing image plane are provided and distance data obtained by the distance sensors for each object in each area is supplied to a main object detection circuit and a normalizing circuit. The normalizing circuit normalizes the distance data into a real number ranging from 0 to 1 and then supplies the same to a neural network. The neural network formed of a single-layered neuron units of which the synapse connection weighting factors are previously obtained by the learning process, calculates a vector difference between the distance data and the synapse connection weighting factors of each neuron unit, detects the minimum vector difference, and outputs position data of a main object corresponding to a neuron unit which gives the minimum vector difference. The position data of the main object is input to a main object detection circuit. One of the outputs from the distance sensors corresponding to the main object is selected by the main object detection circuit and is supplied to a focus detection circuit for effecting the calculation to detect the focus. An output of the focus detection circuit is supplied to a lens driving mechanism so as to adjust the focus.
Automatic camera