Many first-grade undergraduate classes give instructions on report writing to improve students' ability to output the material that is learned. Previous studies on expository writing have suggested that informing the writers about the potential readers could improve the legibility of written texts. What kind of readers should writers assume in order to produce a report that is easiest to understand? We constructed a scale for assessing the audience awareness of writers when writing reports. Exploratory factor analysis was conducted on evaluations of undergraduates (N = 156). Results indicated that the scale consisted of seven factors: "No audience awareness", "Experts", "People setting the topic of the report", "General readers", "Evaluators", "Teachers", and "Busy people". Confirmatory factor analysis of the factors indicated acceptable values. Then, participants were classified into high and low score groups based on the frequency of writing reports and on their feelings regarding report writing self-efficacy. The mean evaluations for each factor were compared between the two groups. Dividing by frequency indicated that the low group showed significantly higher values than the high group for No audience awareness and General readers, whereas the high group showed significantly higher values for People setting the topic of the report, Teachers, and Experts. Moreover, dividing by feelings of efficacy indicated that the low group showed higher values than the high group for No audience awareness and Evaluators.