A self-position calculating apparatus comprising: a light projector installed in a vehicle, and configured to project a patterned light beam (32a, 32b) onto a road surface around the vehicle; and an image capturing unit installed in the vehicle, and configured to capture an image of the road surface around the vehicle including an area onto which the patterned light beam (32a, 32b) is projected; an orientation angle calculator configured to calculate an orientation angle of the vehicle relative to the road surface from a position of the patterned light beam (32a, 32b) on the image obtained by the image capturing unit; and the self-position calculating apparatus being characterized by an orientation change amount calculator configured to calculate an amount of change in orientation of the vehicle based on temporal changes in a plurality of feature points (Te) on the road surface which are detected from the images obtained by the image capturing unit; a self-position calculator configured to calculate the current position and orientation angle of the vehicle by adding the amount of change in the orientation to starting points of an integration operation of the vehicle; and a detection condition determining section configured to determine whether the condition under which the plurality of feature points (Te) are detected by the orientation change amount calculator satisfies a first criterion; wherein if the condition does not satisfy the first criterion and if a second criterion is satisfied, the self-position calculator (i) sets (a) the position of the vehicle at that time when the condition does not satisfy the first criterion and satisfies the second criterion, and (b) the orientation angle of the vehicle calculated by the orientation angle calculator as starting points; and (ii) starts to add the amount of change in the orientation to the starting points; wherein the first criterion requires that at least three feature points associated between previous and current images can be detected; and the second criterion requires that the orientation angle calculator succeeds in calculating the orientation angle. a light projector installed in a vehicle, and configured to project a patterned light beam (32a, 32b) onto a road surface around the vehicle; and an image capturing unit installed in the vehicle, and configured to capture an image of the road surface around the vehicle including an area onto which the patterned light beam (32a, 32b) is projected; an orientation angle calculator configured to calculate an orientation angle of the vehicle relative to the road surface from a position of the patterned light beam (32a, 32b) on the image obtained by the image capturing unit; and the self-position calculating apparatus being characterized by an orientation change amount calculator configured to calculate an amount of change in orientation of the vehicle based on temporal changes in a plurality of feature points (Te) on the road surface which are detected from the images obtained by the image capturing unit; a self-position calculator configured to calculate the current position and orientation angle of the vehicle by adding the amount of change in the orientation to starting points of an integration operation of the vehicle; and a detection condition determining section configured to determine whether the condition under which the plurality of feature points (Te) are detected by the orientation change amount calculator satisfies a first criterion; wherein if the condition does not satisfy the first criterion and if a second criterion is satisfied, the self-position calculator (i) sets (a) the position of the vehicle at that time when the condition does not satisfy the first criterion and satisfies the second criterion, and (b) the orientation angle of the vehicle calculated by the orientation angle calculator as starting points; and (ii) starts to add the amount of change in the orientation to the starting points; wherein (i) sets (a) the position of the vehicle at that time when the condition does not satisfy the first criterion and satisfies the second criterion, and (b) the orientation angle of the vehicle calculated by the orientation angle calculator as starting points; and (ii) starts to add the amount of change in the orientation to the starting points; wherein the first criterion requires that at least three feature points associated between previous and current images can be detected; and the second criterion requires that the orientation angle calculator succeeds in calculating the orientation angle.