In a word: no.
Methylphenidate [MPH] (trade names: Ritalin, Concerta, etc.) is a psychostimulant used in treating individuals with a diagnosis of ADHD in some countries. Neither MPH nor any type of amphetamine-type psychostimulant is lawfully prescribed for the treatment of adult ADHD in Japan.
The lawful use of MPH in Japan is covered by MHLW notices 1026001,1026002, 1026003 issued on 26 Oct. 1997. In principle, the use of MPH for adult ADHD was never allowed in Japan. Currently, the only legal use for MPH in adults is narcolepsy (Ritalin,) and to treat ADHD in children age 6-13 (Concerta.)
Formerly, MPH was used for depression, and this led to abuse, so that use was banned in 2008. A document submitted 29 Nov. 2007 from the Japan Psychiatry Association Ritalin Special Board to the MLHW recommended tapering off over 6 weeks while substituting with antidepressants, therapy, or Pemoline.
The status of MPH for personal importation is unclear, the Yakkan Shomei packet states that one will not be granted for MPH. Importing MPH illegally is a violation of the Controlled Substances Control Law, and carries a penalty of years at hard labor if discovered.