In industrial cooling crystallization, knowledge of scale formation is important because this phenomenon becomes a cause of decreased heat exchange coefficient and productivity loss. However, only a few studies investigating the dynamic change of scale formation have been reported. The present study focuses on crystallization and scale formation dynamics which occur during the cooling operation at the start-up of melt crystallization. Methacrylic acid containing 5 wt% of MeOH was linearly cooled with a cooling coil and the crystallization phenomenon was observed dynamically. During crystallization, five crystallization processes were newly observed: (i) nucleation in melt bulk, (ii) rapid formation of bulky scale on the surface, (iii) temperature increase and loss/disappearance of suspension crystals, (iv) dissolution of bulky scale, and (v) growth of dense layer scale. Since dynamic scale formation in the initial stage of start-up operation became clear, it is expected that these results will be useful for designing the start-up operation.