The Mikawa Bay Region, central Japan, is characterized by many active faults recording Quaternary activity. It is, however, difficult to understand the overall tectonic character of the region due to the thick sediments in this region. We estimated the depth and the structure of the basement top in the Mikawa Bay Region through the analysis of gravity data, compiling publicly available gravity data and our own gravity measurements in the central part of the region. The gravity basement map shows the deepening of the basement top from the Nishi-Mikawa Plain to the Chita Peninsula. Two-dimensional modeling constrains the orientation of the Utsumi and Takahama faults. The fact that the basement top structure related to the Kou Fault is insignificant in the gravity data indicates that the geometry of the Kou Fault is small relative to that of the Utsumi Fault. The basement top structure from the Nishi-Mikawa Plain to the Chita Peninsula reveals a half graben structure bounded by the Utsumi Fault. The inverse motion of the Utsumi Fault, which underwent normal faulting during the Miocene followed by recent reverse faulting, is interpreted to reflect the inversion tectonics of the half graben. The timing of the inversion tectonics, i.e. the reverse faulting of the Miocene normal fault, can be compared to an episode of basin inversion observed at the eastern margin of the Japan Sea, northeastern Japan. The Takahama Fault in the center of the Nishi-Mikawa Plain is considered to have formed as a result of the backthrust of the Utsumi Fault under inversion tectonics. If the Takahama Fault is indeed the backthrust fault of the Utsumi Fault, the root of the Takahama Fault may be deep such that the Takahama Fault is seismogenic and linked to the 1945 Mikawa earthquake.