This is the Toontown home of Mickey Mouse himself. Inside, you can pose for a picture with Mickey, and afterwards walk around and explore his home.
Many, many Japanese people (at least the ones that visit Tokyo Disneyland) love Mickey Mouse to no end. Although Mickey makes public appearances at several locations throughout the park, it's almost impossible to get a photo alone with him, as he is constantly mobbed by adoring fans. A visit to Mickey's House is probably the only way to get a picture alone with Mickey, and for this reason lines for Mickey's House are almost always longer than those for just about any other attraction at Tokyo Disneyland—including Space Mountain. Wait times on busy days can be 90 minutes or more. Unless you absolutely must have a photo with Mickey Mouse, you should probably skip visiting Mickey's House and spend your time enjoying other areas of the Park.