An altitude detecting unit for detecting altitude of a running vehicle along a test running route, the altitude detecting unit comprising: a reception circuit that is configured to receive data indicating altitude of the vehicle from a satellite positioning system receiver, and data indicating pressure around the vehicle from a pressure sensor, the satellite positioning system receiver and the pressure sensor both being mounted on the test vehicle during running of a test; a conversion expression generating circuit that is configured to generate a conversion expression for converting the data indicating pressure around the vehicle from the pressure sensor, into data indicating the altitude of the vehicle; and an altitude calculation circuit that is configured to convert the data indicating pressure around the vehicle based on the conversion expression into data indicating altitude, and to thereby calculate the altitude of the vehicle at a part of or along the whole of the test running route of the vehicle, the altitude detecting unit being configured such that at each one of multiple predetermined valid altitude measurement points at which valid altitude data is outputted from the receiver along the test running route, pressure altitude, that is altitude obtained by converting pressure data using the conversion expression, is made substantially equal to altitude indicated by valid altitude data, characterized in that for a satellite positioning invalid section, being a section where valid altitude data is not outputted from the receiver, the conversion expression generating circuit regards a point just before and a point just after a satellite positioning invalid section as such predetermined valid altitude measurement points, and the conversion expression generating circuit generates a conversion expression corresponding to the satellite positioning invalid section based on the valid altitude measurement points wherein said conversion expression is generally given by a linear expression of the form y = Ax + B, wherein y represents altitude, x represents pressure, A represents a relationship between a change in altitude and a change in pressure, and B represents an offset, wherein an offset value BS1 of the conversion expression is a value that equals the difference between the GPS altitude indicated by the receiver at the just-before point and the altitude by the pressure sensor, and an offset value BE1 of the conversion expression is a value that equals the difference between the GPS altitude indicated by the receiver at the just-after point and the altitude by the pressure sensor, and wherein from the just-before point toward the just-after point, an offset value of the conversion expression for the respective points in the first satellite positioning invalid section is set to monotonously increase (for BS1 < BE1) or monotonously decrease (for BS1 > BE1). a reception circuit that is configured to receive data indicating altitude of the vehicle from a satellite positioning system receiver, and data indicating pressure around the vehicle from a pressure sensor, the satellite positioning system receiver and the pressure sensor both being mounted on the test vehicle during running of a test; a conversion expression generating circuit that is configured to generate a conversion expression for converting the data indicating pressure around the vehicle from the pressure sensor, into data indicating the altitude of the vehicle; and an altitude calculation circuit that is configured to convert the data indicating pressure around the vehicle based on the conversion expression into data indicating altitude, and to thereby calculate the altitude of the vehicle at a part of or along the whole of the test running route of the vehicle, the altitude detecting unit being configured such that at each one of multiple predetermined valid altitude measurement points at which valid altitude data is outputted from the receiver along the test running route, pressure altitude, that is altitude obtained by converting pressure data using the conversion expression, is made substantially equal to altitude indicated by valid altitude data, characterized in that for a satellite positioning invalid section, being a section where valid altitude data is not outputted from the receiver, the conversion expression generating circuit regards a point just before and a point just after a satellite positioning invalid section as such predetermined valid altitude measurement points, and the conversion expression generating circuit generates a conversion expression corresponding to the satellite positioning invalid section based on the valid altitude measurement points wherein said conversion expression is generally given by a linear expression of the form y = Ax + B, wherein y represents altitude, x represents pressure, A represents a relationship between a change in altitude and a change in pressure, and B represents an offset, wherein an offset value BS1 of the conversion expression is a value that equals the difference between the GPS altitude indicated by the receiver at the just-before point and the altitude by the pressure sensor, and an offset value BE1 of the conversion expression is a value that equals the difference between the GPS altitude indicated by the receiver at the just-after point and the altitude by the pressure sensor, and wherein from the just-before point toward the just-after point, an offset value of the conversion expression for the respective points in the first satellite positioning invalid section is set to monotonously increase (for BS1 < BE1) or monotonously decrease (for BS1 > BE1).