April 2018 is the 51st month of the PlayStation 4 being on sale in Japan. The gap grew in favor of the PlayStation 3 by 62,656 units in the last month and in favor of the PlayStation 4 by 422,834 units in the last 12 months. The PlayStation 4 currently leads by just 351,681 units.
The PlayStation 3 launched in November 2006, while the PlayStation 4 launched in February 2014. The PlayStation 4 has sold 6.63 million units, while its predecessor the PlayStation 3 sold 6.28 million units.