An input voltage control device (1A, 1B, 1C) comprising: a first power line to which a first potential is applied; a second power line divided into one part and an other part, wherein a second potential is applied to said one part characterized by a third power line; a constant voltage generator configured to operate on the first potential supplied by said first power line and the second potential supplied by said one part of the second power line and configured to output to said third power line a third potential having a constant potential difference from said second potential; a reference potential generator (3A, 3B) connected to said third power line and said one part of the second power line, configured to generate a reference potential on the basis of said third potential and said second potential and configured to output said reference potential; a comparative potential generator (4A, 4B, 4C) connected to said first power line and said one part of the second power line, configured to generate a comparative potential on the basis of said first potential and said second potential and configured to output said comparative potential; a comparator configured to operate on the third potential supplied by said third power line and the second potential supplied by said one part of the second power line and alternately configured to output a conducting potential or an interrupting potential depending on a comparison between said reference potential and said comparative potential; and a semiconductor device with one terminal of its current path connected to said one part of the second power line, another terminal connected to said another part of the second power line and a control terminal connected to an output terminal of said comparator, the semiconductor device configured to make said current path conductive when the conducting potential is inputted to said control terminal and non-conductive when the interrupting potential is inputted to said control terminal. a first power line to which a first potential is applied; a second power line divided into one part and an other part, wherein a second potential is applied to said one part characterized by a third power line; a constant voltage generator configured to operate on the first potential supplied by said first power line and the second potential supplied by said one part of the second power line and configured to output to said third power line a third potential having a constant potential difference from said second potential; a reference potential generator (3A, 3B) connected to said third power line and said one part of the second power line, configured to generate a reference potential on the basis of said third potential and said second potential and configured to output said reference potential; a comparative potential generator (4A, 4B, 4C) connected to said first power line and said one part of the second power line, configured to generate a comparative potential on the basis of said first potential and said second potential and configured to output said comparative potential; a comparator configured to operate on the third potential supplied by said third power line and the second potential supplied by said one part of the second power line and alternately configured to output a conducting potential or an interrupting potential depending on a comparison between said reference potential and said comparative potential; and a semiconductor device with one terminal of its current path connected to said one part of the second power line, another terminal connected to said another part of the second power line and a control terminal connected to an output terminal of said comparator, the semiconductor device configured to make said current path conductive when the conducting potential is inputted to said control terminal and non-conductive when the interrupting potential is inputted to said control terminal.