To prevent the occurrence of image blurring owing to blurring by making at least a second or a third lens group an image blurring correction system which can be changed to a direction vertical to an optical axis, and satisfying a specified condition.

An objective optical system OL is constituted of a first lens group having positive power constituted of a first L1 and a second lens L2, which are mutually connected, a second lens group having negative power constituted of a third lens L3 single body and a third lens group having positive power constituted of a fourth lens L4 single body. The third lens L3 (the second lens group of the objective optical system OL) and the fourth lens L4 (the third lens group of the objective optical system OL) of the fourth lens L4 are the image blurring correction systems which can be changed in the direction vertical to the optical axis O. They satisfy condition expressions 0.1<d1-2/f0 and 0.7<f0/f1<3. Then, d1-2 is a distance between the first lens group and the second lens group, f0 is the synthesis focus distance of the objective optical system OL and f1 is the focus distance of the first lens group.