A numerical simulation model of brittle crack propagation was developed incorporating fracture surface irregularity, and small-scale crack arrest experiment of a steel plate was conducted to validate the model. Mechanisms of the formation of brittle fracture surface irregularities including chevron markings in the steel were discussed based on the model calculations and the experiment. Formation of the chevron markings was found to depend on applied stress intensity factor. The model calculations and the experiment showed that the chevron markings are nucleation and continuation of ridges, which are formed between two cleavage crack terraces with different height levels. The dependence of the extent of the chevron markings on applied stress intensity factor is understood as that a deep ridge reduces local stress intensity factor by shear stress acting on the ridge, and the deep ridge can develop only at high stress intensity factor level but only shallow ridges are possible if stress intensity factor level is low. This tendency agreed between the experiment and the calculation. Relationship between crack arrest toughness and fracture surface irregularities is discussed.