Pylodin 6 J is commonly used to evaluate the wood density of standing trees in forest tree breeding. However, when applied to young or small trees, the pin penetration used in measurements can cause significant damage, adversely affecting their subsequent growth. This study aimed to evaluate the wood density of standing trees using Pylodin 4 J, which reduces the spring energy of pin penetration from 6 J to 4 J and employs a thinner pin diameter, decreased from 2.5 mm to 2.0 mm. The investigation involved 187 cutting trees derived from 38 full-sib individuals of Cryptomeria japonica, 8 years after planting. Pin penetration depths measured with Pilodyn 4 J were compared to those obtained using the conventional 6 J. The average pin penetration depth with Pylodin 4 J was 3.17 mm greater than that of 6 J. Although some individual trees exhibited large differences in pin penetration depths between 4 J and 6 J, the correlation coefficients were high: 0.887 for individual values and 0.965 for clone values. The repeatability values for both instruments were similar. These findings suggest that Pylodin 4 J was comparable to 6 J for clonal evaluation of wood density.