A lens optical system includes a first optical system which includes, in order from an object side to an image side along an optical axis, a first lens group having a positive refractive power and including a first reflection member to redirect an optical path of light representing an object from a first direction toward an image sensor, a second lens group having a negative refractive power, a third lens group having a positive refractive power, a fourth lens group having a positive refractive power, and a fifth lens group having a positive refractive power. During zooming from a wide mode to a tele mode, the first lens group and the fifth lens group are fixed, the second lens group moves toward the image side, the third lens group and the fourth lens group move toward the object side, and the fourth lens group performs focusing.