3. An operation assisting device comprising: a keyword detector that compares voice data with preliminarily stored keywords associated with an operation target and determines whether the voice data match with the preliminarily stored keywords or not; and a sight-line detector that detects whether or not sight lines of a speaker are directed at the operation target only when it is determined that the voice data to not include the preliminarily stored keywords, an the similarity between or among the voice data falls within a predetermined range, wherein the keyword detector determines that the voice data match with the preliminarily stored keywords in a case where the similarity between or among the voice data is within the predetermined range during a predetermined time period before a timing when the sight-line detector detects that the sight lines of the speaker are directed at the operation target.
3. An operation assisting device comprising: a keyword detector that compares voice data with preliminarily stored keywords associated with an operation target and determines whether the voice data match with the preliminarily stored keywords or not; and a sight-line detector that detects whether or not sight lines of a speaker are directed at the operation target only when it is determined that the voice data to not include the preliminarily stored keywords, an the similarity between or among the voice data falls within a predetermined range, wherein the keyword detector determines that the voice data match with the preliminarily stored keywords in a case where the similarity between or among the voice data is within the predetermined range during a predetermined time period before a timing when the sight-line detector detects that the sight lines of the speaker are directed at the operation target. 6. The operation assisting device according to claim 3 , wherein the keyword detector further calculates an evaluation value indicating a likelihood that the voice data match with the preliminarily stored keywords, and determines that the voice data match with the preliminarily stored keywords, in a case where the calculated evaluation value is greater than or equal to a predetermined threshold value.