High-temperature confocal laser scanning microscopy (HT-CLSM) is an in-situ direct observation device of crystallization behaviors in metals, and silicates (slag, flux, etc.) 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 behavior in the liquid steel, slag crystallization, etc. A few examples performed in KTH will be summarized. 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 steel are given. The pros and cons of HT-CLSM applied in physical metallurgy are summarized. Last but not least, the combinational approach using HT-CLSM supplemented with other methodologies, e.g. large-scale facility is briefly discussed. This work aims to extend the application of this in-situ observation methodology in comprehensive metallurgy.