Experiments for doubly strange hypernuclei with nuclear emulsion have been performed at KEK and J-PARC for the past 30 years. From detected 47 events, the characteristics were understood for Λ-Λ interaction to be weakly attractive, linear mass number dependence for two Λs binding energy, presence of Ξ hypernucleus, and it can be seen for something like the level structure of 15ΞC. Developing scanning method, so-called overall-scanning method, probably presents more rich information on not only doubly strange hypernuclei but also single-Λ hypernuclei.