A loop heat pipe (LHP) is used as the heat transport device to reject heat from the Monitor of All-sky X-ray Image (MAXI). Since this LHP was designed exclusively for the MAXI system, it is different from conventional LHPs in configuration, a double-condenser design. We experimentally investigated the effects of the particular design of this LHP on the heat transfer performance by using the LHP Ground Test Unit (GTU) on the ground. The steady heating experiment was carried out to investigate the steady state performance of LHP. When the two condensers were cooled at different temperatures under a steady heating condition, a quasi-periodic temperature oscillation was observed in the evaporator and accumulator area. We experimentally investigated the cause and mechanism of the temperature oscillation.