In wastewater treatment equipment, a surfactant is added to a micronanobubble reaction vessel 3 by using a surfactant pump 8 and a surfactant tank 9 which constitute a surfactant adding section. Thereby, a micronanobubble generator 4 stably and efficiently produces micronanobubbles in the treatment water as raw water containing the surfactant in the micronanobubble reaction vessel 3. Thus, the micronanobubbles make it possible to efficiently pretreat the wastewater introduced into the micronanobubble reaction vessel. Consequently, it becomes possible not only to enhance efficiency of wastewater treatment but also to reduce a treatment load on wastewater treatment equipment 14 in a step subsequent to the pretreatment. Thereby, scale of the wastewater treatment equipment 14 is reduced.