Economic situation of Polish farms upon accession to the European Union is subject to systematic improvement. Due to availability of additional sources of funding, farmers have started implementation of the most modern technologies and machines in the agricultural production processes. Increase of the work safety level expressed with a decreasing number of accidents in the country is indirectly a positive effect of these changes. In order to carry out more precise analysis of this phenomenon, questionnaire research was performed on the randomly selected group of 180 agricultural farms in Łódzkie and Dolnośląskie Voivodeship. The questionnaire was composed of open and closed questions referring to the assessment of the safety level of farmers' work in relation to their investment activity as one of several factors which decrease the accident risk. According to the research, the main investment purpose of farmers was modernization of technical infrastructure and improvement of the safety level of labour. Tractors, sprayers and trailers prevailed among the most frequently purchased machines. In both farms, it was found out that the value of the implemented investments in 2006-2012 is inversely proportional to the number of accidents registered in agricultural farms. Suggested mathematical formulas developed based on the collected data prove that the decrease in the number of accidents in agricultural farms is considerably determined by the implemented investments.