To provide a circuit board and an ion generator in which noises are prevented at an inexpensive method.

A circuit board 3 comprises: a substrate 20 having a surface; and a ceramic capacitor with an approximate rectangular parallelepiped shape provided on a main surface. The substrate 20 includes a mounting region 31 in which the ceramic capacitor is mounted, and the capacitor includes a first side face and a second side face opposed in a shorter-side direction of the ceramic capacitor, and a third side face and a fourth side face opposed in a longitudinal direction of the ceramic capacitor. An outer peripheral edge of the mounting region 31 includes a third side section extending along the third side face, a first side section extending along the first side face from a first end of the third side section, and a second side section extending along the second side face from a second end of the third side section.