TOKYO -- Hidekazu Nishikido, a 24-year-old agent at a staffing company, recently got promoted to help manage a small group of employees. The new job means a higher salary and a better title.

But he isn't happy about it. Now he often works past 10 p.m., leaving him less time with his girlfriend. So Mr. Nishikido flatly told his bosses at R-live Inc. he isn't interested in further promotions.

"My...