1. An apparatus for determining the attitude of an artificial satellite comprising: one or a plurality of star sensors; a star catalog data base in which information on each of stars in an inertial coordinate system is stored; a star identification section in which star images output from said star sensors are collated with a star catalog in said star catalog data base with respect to each star sensor to output a group of corresponding candidates; an attitude computation section for computing a value of an attitude candidate of the artificial satellite with respect to each corresponding candidate; an attitude updating section for updating the value of the attitude candidate on the basis of star images output from the star sensor and the star catalog; an attitude propagation section for computing the value of the attitude candidate at the present sampling time from the value of the attitude candidate at a preceding sampling time and the artificial satellite body angular velocity; and an attitude candidate unification section for comparing the values of a plurality of attitude candidates to combine the same into one, said attitude candidate unification section being provided in a loop formed by said attitude updating section and said attitude propagation section.