According to online research site Nensyu Labo, here is a list of the mean yearly income for the game industry with numbers crunched from public reports filed by the companies.
Square Enix: ¥21,680,000 (US$272,988)
Sony: ¥9,230,000 ($US116,189)
Nintendo: ¥9,140,000 ($US115,032)
Sega Sammy: ¥8,220,000 ($US103,486)
Konami: ¥6,780,000 ($US85,371)
Namco Bandai: ¥6,400,000 ($US80,577)
Tecmo Koei: ¥6,150,000 ($US77,418)
Capcom: ¥5,710,000 ($US71,891)
A couple things to keep in mind: The strong yen makes the salaries appear much larger in US dollars. Also, this doesn't necessarily mean your typical Square Enix employee is earning $US200k. Rather, it probably means there is a layer of upper and mid-management with very high salaries.
The ranking also showed which game developers brought up the rear of the pack — namely folks like Nippon Ichi Software (3,700,000 or $US46,512) and Tose (¥3,500,000 or $US43,995). Give those people raises!