Japan Small Vehicle Engine Co., Ltd./Kyoritsu Motor Co., Ltd., Minato-ku, Tokyo, 1952-55(?)
日本小型自動車発動機㈱/共立発動機
Japan Small Engine/Kyoritsu Motor produced 150cc and 250cc ohv machines along with 250cc and 295cc sv machines. All were single cylinder machines sold under the NewJap (ニュージャップ号) brand name. I'm not sure why two company names are listed for the one brand, and have not been able to locate a company history, so no further information is available at this time.
Note there is a Kyoritsu company located in Hamamatsu City that made the 'Rush' in 1953 (see this link), so my assumption is that it not the same company as this one.