1. A signal processing device, comprising: a memory; and a processor coupled to the memory and configured to: receive time series information related to an operation of a user from a camera, extract first time series information from the time series information, determine whether the first time series information is recognized as a particular type of operation, based on a recognition condition, extract second time series information prior to the first time series information from the time series information when the first time series information is recognized as the particular type of operation according to the determining, the second time series information being similar to the first time series information, change the recognition condition so that the second time series information is recognized as the particular type of operation, and execute a recognition processing to another time series information based on the changed recognition condition, when the another time series information is received from the camera.