An immersion microscope objective formed of thirteen or fewer lens elements includes, in order from the object side, first and second lens groups of positive refractive power, a third lens group, a fourth lens group having negative refractive power with its image-side surface being concave, and a fifth lens group having positive refractive power with its object-side surface being concave. The first lens group includes, in order from the object side, a lens component that consists of a lens element of positive refractive power (when computed as being in air) and a meniscus lens element having its concave surface on the object side. Various conditions are satisfied to ensure that images of fluorescence, obtained when the immersion microscope objective is used in a laser scanning microscope that employs multiphoton excitation to observe a specimen, are bright and of high resolution. Various laser scanning microscopes are also disclosed.