The population of sika deer, in Shiga Prefecture, has increased recently. It is said that the deer have caused damage to tea fields in Koka City (a major tea-producing area in Shiga Prefecture). However, we cannot understand the situation in detail. For this reason, we conducted a questionnaire survey for farmers in July 2016, and we did a tea field survey from September 2016, as well.Firstly, the results of the questionnaire survey showed approximately 60% of the farmers recognized that sika deer have been a bad influence in young arboretums, and approximately 90% of the farmers recognized this in mature orchards.Secondly, the results of field surveys showed that invasion by the sika deer have fed on the undergrowth in the tea fields. But, in late October (the amount of undergrowth had become less), and we often saw sika deer feeding on the tea leaves.In addition, many farmers asserted that applied organic fertilizer attracts sika deer to tea fields, Thus, we researched the feeding habits of sika deer, and as a result, we saw aggressive foraging behavior of sika deer in tea fields to organic fertilizer (for instance, rapeseed oil cake and fish meal). However, the sika deer did not feed on castor oil cake during the observation.