The endogenous fertility model is often considered in conjunction with the pay-as-you-go (PAYG) pension system. This is because, in a PAYG pension system, the birth rate affects the rate of return on pensions. In addition to the birth rate, the income level of the working generation is also an important factor to consider in the operation of a PAYG pension system. With this in mind, this chapter examines human capital as a consideration of income levels. Human capital is generated through educational investment, and in this chapter, it is assumed to be created through educational investments in children. The objective is to examine how parents decide the number of children and the quality of children (where quality refers to the level of human capital) within the framework of the endogenous fertility model. Pension benefits can be provided through either a defined benefit or a defined contribution method. This chapter aims to clarify how the differences between these two methods of providing benefits affect the birth rate.