A breast pump according to the present invention includes a variable pressure generating unit, the variable pressure generating unit including a power driving unit including a stepping motor that is capable of rotating both normally and in reverse, and a negative pressure forming unit that creates a negative pressure state periodically by causing an elastic body to deform in accordance with a cycle period formed by the power driving unit, wherein the negative pressure forming unit is coupled to the expressing unit, and the stepping motor is capable of modifying an amplitude of the cycle period and the cycle period during negative pressure formation as desired. Hence, a suction pressure and a pressure increase/decrease cycle can both be set as desired, and moreover, a breast pump that uses electric power can be constructed compactly.
