TOKYO—Mitsubishi Electric’s CEO said he will step down to take responsibility for “three decades of systematic deceit” during which the Japanese firm falsified inspection data for air conditioners and brake compressors used in trains. The admission by Mitsubishi, whose products range from air conditioners and vacuum cleaners to industrial printers and satellites, further dents Japan’s reputation for high-quality manufacturing, already tarnished by other cases of companies falsifying or covering up test data. “I am shocked by this,” Takeshi Sugiyama told a news conference, at which he apologized for the falsification and promised to appoint a successor as early as this month once he had helped coordinate the company’s response to the problem. Sugiyama, who became CEO in 2018 and has been with Mitsubishi for more than four decades, said on Friday he regretted not informing shareholders at its annual meeting on June 29. Mitsubishi management was aware of the air …