Recently, several countries have established a national forest survey and monitoring system to analyze the exact amount of forest resources and identify changes in forest ecosystems. South Korea is also collecting data on basic forest statistics and conducting surveys to assess the health of forests. The most basic part of a forest survey has many subsequent effects in related work and in the work of actual measurers and information users. Therefore, accurate results are important because these results are the basis for the development of forest-related research. The diameter at breast height (DBH) is a measurement item for forest investigation, and it is the most basic data among the essential items of forest management, forest inventory, and carbon cycle modeling. DBH measurements have traditionally been made manually using calipers. However, this method can cause errors depending on the person and has a disadvantage that it is difficult to measure DBH when the shape of the tree is irregular. In existing forest research, there is a lack of research on this measurement method. As an emerging technology, 3D laser scanning has been introduced in the field of forestry, and its use is expected. In this study, a 3D laser scanner was used to measure DBH and tree height. Data on the forest studied were obtained using a handheld scanner. Software measurements were also performed on felled trees to obtain data, which were compared with those obtained using calipers. The DBH measurements showed a deviation of less than 4 cm from the caliper measurements. These results indicate that DBH can be measured using a handheld scanner. Also, measuring a tree diameter at a height of 1.2 m is difficult in the field; thus, using a handheld scanner will improve work efficiency. The tree heights measured using a handheld scanner were within 10 cm of the reference values. Although the reference values were measured using a total station for accurate measurement, an error is likely to occur when using a clinometer in the field, and tree height measurement using a handheld scanner may improve the measurement accuracy. Also, the diameters of felled trees were measured. The diameters of the felled trees measured using a scanner showed a difference of less than 4 cm from the reference values. There is a slight difference from the values measured using calipers or a tape, which may be due to the noise of the point cloud. If further research is performed to reduce noise and automate the measurement, it may be possible to use a scanner-based method to measure the diameters of felled trees.