DECIGO Pathfinder (DPF) is a spacecraft that will test, in space, the technologies required to realize DECIGO. These technologies include (1) Drag-free spacecraft, (2) Frequency-stabilized laser, and (3) Fabry-Perot cavity control. In addition, DPF can have a role as a scientific mission. DPF could detect gravitational waves coming from the coalescence of intermediate-mass black hole binaries in our galaxy. Also, it could measure the distribution and variation of the gravitational field of the earth. Consequently, DPF is one of the important mission candidates for the small science spacecraft series run by JAXA/ISAS.