Logarithmic étale cohomology, II

We introduce the log étale cohomology in the second (full log étale) sense after K. Kato and prove several fundamental results including base change theorems. To prove them, we use some corresponding results in the log étale cohomology in the first (kummer log étale) sense. Conversely, they are used to show some new results in the kummer log étale cohomology.