We have proposed a room temperature, all electrical driving and detecting, very sensitive bolometer using a doubly clamped microelectromechanical (MEMS) resonator, which can be excited and detected by using piezoelectric effect. The device detects the shift in the resonance frequency caused by heating and works as a very sensitive bolometer. The bolometer showed a voltage responsivity about 3,300 V/W, while keeping low noise spectral density of about 60 nV/Hz1/2, demonstrating a noise equivalent power (NEP) of below 20 pW/Hz1/2 at room temperature. Further improvement in NEP is expected by optimizing the sample structure. The observed effect can be used for realizing high-sensitivity terahertz bolometer for room-temperature operation.