Selection for increased resistance to Salmonella carrier-state.

A zoom lens includes three lens units which are a first unit having a negative refracting power, a second unit having a positive refracting power, and a third unit having a positive refracting power arranged in the stated order from the side of an original surface. Zooming is effected by changing an air space between the first unit and the second unit and an air space between the second unit and the third unit. The second unit has a diffractive optical element.