A compound-semiconductor photovoltaic cell comprising: a compound-semiconductor substrate ; one or more first photoelectric conversion cells formed of a first compound-semiconductor material and laminated on the compound-semiconductor substrate ; a first junction layer formed of a second compound-semiconductor material and laminated on the one or more first photoelectric conversion cells; a second junction layer formed of a third compound-semiconductor material and joined to the first junction layer directly or indirectly; and one or more second photoelectric conversion cells formed of a fourth compound-semiconductor material, joined to the one or more first photoelectric conversion cells via the first junction layer and the second junction layer , and arranged on a light incident side of the one or more first photoelectric conversion cells in a light incident direction, wherein band gaps of the one or more first photoelectric conversion cells and the one or more second photoelectric conversion cells are made smaller from the incident side toward a deep side in the light incident direction, in a case of a single second photoelectric conversion cell , a band gap of the second junction layer is greater than a band gap of the second photoelectric conversion cell , and in a case of plural second photoelectric conversion cells , the band gap of the second junction layer is greater than a band gap of at least one second conversion cell of the plural second photoelectric conversion cells , the one or more second photoelectric conversion cells are gallium arsenide (GaAs)-based photovoltaic cells, and characterized in that the second junction layer is a gallium phosphide arsenide (GaPAs) layer. a compound-semiconductor substrate ; one or more first photoelectric conversion cells formed of a first compound-semiconductor material and laminated on the compound-semiconductor substrate ; a first junction layer formed of a second compound-semiconductor material and laminated on the one or more first photoelectric conversion cells; a second junction layer formed of a third compound-semiconductor material and joined to the first junction layer directly or indirectly; and one or more second photoelectric conversion cells formed of a fourth compound-semiconductor material, joined to the one or more first photoelectric conversion cells via the first junction layer and the second junction layer , and arranged on a light incident side of the one or more first photoelectric conversion cells in a light incident direction, wherein band gaps of the one or more first photoelectric conversion cells and the one or more second photoelectric conversion cells are made smaller from the incident side toward a deep side in the light incident direction, in a case of a single second photoelectric conversion cell , a band gap of the second junction layer is greater than a band gap of the second photoelectric conversion cell , and in a case of plural second photoelectric conversion cells , the band gap of the second junction layer is greater than a band gap of at least one second conversion cell of the plural second photoelectric conversion cells , the one or more second photoelectric conversion cells are gallium arsenide (GaAs)-based photovoltaic cells, and characterized in that the second junction layer is a gallium phosphide arsenide (GaPAs) layer. <EOS>