The ambrosia beetle Platypus quercivorus causes mass mortality of fagaceous trees throughout Japan. Previous studies demonstrated low levels of P. quercivorus attack on both thinner trees and re-attacked trees with previous infection history. To determine the causes of the low levels of attack on these trees, the patterns of attack by P. quercivorus were investigated in 35 Quercus crispula trees for two consecutive years. Logistic regression analysis indicated a significant positive effect of tree size on the probability of male beetle flying to trees, although previous infection history was not selected as an explanatory variable in the model. Tree size and previous infection history exhibited significant positive and negative effects, respectively, when both were selected as explanatory variables in a model predicting the probability of male beetle boring holes in trees. These results suggest that P. quercivorus disregards thinner trees, and flies away from trees with previous infection history after approaching.