PURPOSE: To reduce a load on a host CPU and to improve the performance of data processing and statistical processing by providing a transmission converter for monitoring device between the host CPU and a monitoring device.

CONSTITUTION: A converter 2 equipped with at least an auxiliary CPU 21, program memory 22, an image information table 23, input transmission equipment 24, and output transmission equipment 25 are provided, and the conversion procedure of transmission is stored in the converter 2 in advance, and the difference of a transmission system and that of transmission speed are converted. Thereby, the load on the host CPU 1 can be remarkably reduced, and effective transmission speed between the host CPU 1 and the monitoring device 3 can be accelerated, and maintainability can be improved, and also, it is possible to reduce the incremental part of programming of the host CPU even when plural devices in this invention are installed.