An on-board apparatus, comprising: a map data storage means in which map data that include altitude information for predetermined geographical points on roads are stored; a subject vehicle position detection means configured to detect a subject vehicle position; a calculation target geographical point setting means configured to set a calculation target geographical point based upon the subject vehicle position; an altitude information acquisition means configured to obtain altitude information corresponding to two geographical points (31, 32), one of which is present ahead of the calculation target geographical point and apart from the calculation target geographical point by a predetermined separating distance, the other of which is present behind the calculation target geographical point and apart from the calculation target geographical point by the separating distance, from the map data; a road grade calculation means configured to calculate a road grade at the calculation target geographical point based upon the altitude information obtained by the altitude information acquisition means; and a separating distance adjusting means configured to adjust the separating distance in correspondence to the calculation target geographical point, characterized in that: the separating distance adjusting means is further configured to adjust the separating distance based upon at least any one of a type of area where the calculation target geographical point is located, a road type designation corresponding to the calculation target geographical point, and a type of intersection present ahead of or behind the calculation target geographical point. a map data storage means in which map data that include altitude information for predetermined geographical points on roads are stored; a subject vehicle position detection means configured to detect a subject vehicle position; a calculation target geographical point setting means configured to set a calculation target geographical point based upon the subject vehicle position; an altitude information acquisition means configured to obtain altitude information corresponding to two geographical points (31, 32), one of which is present ahead of the calculation target geographical point and apart from the calculation target geographical point by a predetermined separating distance, the other of which is present behind the calculation target geographical point and apart from the calculation target geographical point by the separating distance, from the map data; a road grade calculation means configured to calculate a road grade at the calculation target geographical point based upon the altitude information obtained by the altitude information acquisition means; and a separating distance adjusting means configured to adjust the separating distance in correspondence to the calculation target geographical point, characterized in that: the separating distance adjusting means is further configured to adjust the separating distance based upon at least any one of a type of area where the calculation target geographical point is located, a road type designation corresponding to the calculation target geographical point, and a type of intersection present ahead of or behind the calculation target geographical point. the separating distance adjusting means is further configured to adjust the separating distance based upon at least any one of a type of area where the calculation target geographical point is located, a road type designation corresponding to the calculation target geographical point, and a type of intersection present ahead of or behind the calculation target geographical point.