It is known that high-temperature confocal laser scanning microscopy (HT-CLSM) is an in-situ direct observation device of crystallization behaviours for liquid/solid and solid/solid transformations in metallic materials [1,2]. This facility utilizes a halogen heating lamp focused onto the surface of the specimen in a small crucible. This facility was born 30 years ago, and it is suited for in-situ studies of solidification, inclusion behaviour in liquid steel, slag crystallization, etc. Furthermore, the capability of HT-CLSM used in physical metallurgy, in particular, microstructure evolution in sold-state steels will be discussed. A few examples of low-alloy and stainless steels, Al-alloys and high entropy alloys are given. The pros and cons of HT-CLSM applied in physical metallurgy are summarized. In additional, the combinational approach using HT-CLSM supplemented with other methodologies, e.g. large-scale facility is briefly discussed. This work aims to provide new insights to extend the application of this in-situ observation methodology in a scope of comprehensive metallurgy. The examples of applying HT-CLSM in observing solidification of stainless steels [3] and the incipient melting of cluster in Al-alloys [4] are provided below.