To provide an oil level-adjusting device for a stationary engine, capable of promptly following oil level change and keeping an oil level constant regardless of the degree of oil viscosity.

In this oil level-adjusting device, an oil pan 11 and an oil tank 30 of the stationary engine 10 are connected with each other by piping with control valves, and the control valves are opened/closed in accordance with the oil level in the oil pan 11 to keep the oil level in the oil pan 11 in a predetermined value. Oil circulation piping systems 21, 31 having pumps 22, 32 are provided in the oil pan 11 and the oil tank 30, respectively. An oil temperature-adjusting device 24 is provided in the both oil circulation piping systems 21, 31, respectively. Both oil circulation systems are connected with each other via the piping having the control valves 41, 43. A control means 20 for controlling the oil temperature-adjusting device 24 of the oil circulation piping system in the oil pan 11 and the control valves 41, 43 based on the oil level and oil temperature in the oil pan 11 is provided.