All appeals are dismissed.

The costs of appeal are assessed against the plaintiffs.

The grounds of appeal are examined.

1. As to the ground of appeal No. 1 (related to the universal wage system)

A. 1) In cases where it is deemed difficult to calculate working hours in light of working hours, form and nature of work, the principle of wage payment pursuant to the so-called comprehensive wage system, which provides that the amount included in statutory allowances shall be paid as monthly wages or daily wages without calculating the basic wage in advance between the employer and the employee, and that it shall be paid regardless of the number of working hours, is valid when concluding a wage payment contract based on the so-called comprehensive wage system with the purport that it would otherwise be paid to the employee regardless of the number of working hours (see, e.g., Supreme Court Decisions 2002Da16958, Jun. 14, 2002; 208Da6052, May 13, 2010; 2008Da6052, May 13, 2010). However, in such cases, when an agreement entered into between the aforementioned method of wage payment and the employee under the aforementioned comprehensive wage system falls short of the statutory standard of wage payment under the Labor Standards Act, including comprehensive wage payment of 20.