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                                                                       Exhibit 4

                               ADDENDUM NUMBER ONE
                                       TO
                           MONTHLY STOCK PURCHASE PLAN
                             FOR INDEPENDENT AGENTS

         This Addendum Number One to the Monthly Stock Purchase Plan for
Independent Agents of State Automobile Mutual Insurance Company and its
affiliated companies amends the section captioned Dividend Disbursements in the
"Introduction to Plan Document" and the "Plan Document," both to read as
follows:

         Dividends earned on shares in the Participant's account, as they become
         payable by the Company, will be remitted by the Bank to each
         Participant by check, or reinvested by the Bank pursuant to the
         Company's Dividend Reinvestment Plan, provided the Participant has
         enrolled in the Dividend Reinvestment Plan.


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                           MONTHLY STOCK PURCHASE PLAN
                             FOR INDEPENDENT AGENTS


INTRODUCTION TO PLAN DOCUMENT

         The Monthly Stock Purchase Plan for Independent Agents of State
Automobile Mutual Insurance Company, and its affiliated companies (the "Plan")
offers eligible independent agents of State Auto ("Participants") the
opportunity to purchase common stock of State Auto Financial Corporation (the
"Company"), State Auto's publicly held subsidiary, through deductions from
commissions paid by State Auto or its subsidiaries. All costs and service
charges incurred in connection with the purchase of shares through the Plan will
be paid by the Company. Participation is voluntary, and Participants may enroll
in the Plan or withdraw from the Plan at any time, subject to the terms of the
Plan.

         The Plan provides you, as agents, with an opportunity to participate
financially in the future of State Auto Financial Corporation, and to do so
conveniently and without paying brokerage commissions when shares are bought for
your account. A portion of your agent commissions will be automatically deducted
for you each month under the Plan, and these funds will be used (together with
those of other Participants) by National City Bank (the "Bank") to purchase the
Company's common stock at market prices for your account.

         The relationship between each participant and the Bank is the
relationship of client and broker/agent, and neither State Auto, the Company,
nor any of their affiliates assumes any responsibility for or serves in any
capacity in this relationship. In seeking the benefits of share ownership in the
Company, each participant must also accept his or her own investment risks.

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Market values are subject to fluctuations caused by any number of factors, both
internal and external. Therefore, under the Plan, there is no guarantee against
financial loss.

         Shares are purchased at market prices current at the time of purchase
through individual Monthly stock Purchase Plan accounts opened by Participants
at National City Bank. To open a Monthly Stock Purchase Plan account
("account"), fill out the enclosed Commission Deduction Authorization and
Purchase Order forms and return them to the Company in the return envelope
provided. If you have any questions, please contact the Corporate Trust
Department of National City Bank either by telephone (216/575-2658) or by mail
at the address contained in this folder.

ELIGIBILITY

         All principals of active agencies entitled to commissions from State
Auto and its property casualty insurance subsidiaries are eligible to
participate.

HOW THE PLAN WORKS

         Subject to the Monthly Stock Purchase Plan and the Agency Engagement,
National City Bank (the "Bank") will open and maintain accounts in the names of
Participants who so request and will make purchases and sales of shares of
Company common stock for the account of such Participants.

         Funds received by the Bank from (1) commission deductions and (2)
additional voluntary payments up to a maximum of $10,000 per month will be
commingled with those of other Participants in the Plan and used to purchase
shares of Company common stock on a monthly basis. Such shares, including
fractional shares carried to three decimal places, will be credited to each
Participant's account.

         The Company will pay the service charges and brokerage commissions for
purchases of stock. The brokerage commissions and service charges due to the
Bank in connection with the subsequent sale of any shares will be payable by the
Participant.

         Each time shares are purchased for a participant's account, the
Participant will receive from the Bank a detailed statement of the account
showing funds invested from commission deductions and cash payments received,
shares purchased, price per share and total shares held for the Participant. The
statement will include a detachable form to be used to give the Bank notice of a
change of address, instructions for the sale or withdrawal of shares, or to
deposit cash payments. (A check or money order should be made payable to
National City Bank.)

         Commission deductions and cash payment held by the Bank will be used to
purchase shares on the 10th day of that month or the next business day
immediately following if the 10th is not a business day. Timing of cash payments
should be made accordingly. No interest will be paid on cash in the account.

         The shares purchased will be held in safekeeping by the Bank until
termination of a Participant's participation in the Plan. This convenience
provides protection against any loss,


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theft or destruction of share certificates. However, upon a Participant's
written request, the Participant may obtain a certificate for any full shares in
the account.

         Each Participant in the Plan will direct the voting of all full and
fractional shares in the account and will receive all literature sent to the
Company's shareholders.

HOW TO PARTICIPATE

         To participate in the Plan, the Participant must complete and sign both
the Commission Deduction Authorization and the Purchase Order form and mail them
to State Auto in the enclosed postage-paid return envelope. State Auto will
submit the Commission Deduction Authorization and Purchase Order to the Bank
which will open the Participant's account.

COMMISSION DEDUCTION AUTHORIZATIONS

         In the Commission Deduction Authorization, specify the amount to be
withheld from commission disbursements. The minimum amount a Participant can
have withheld is $50 per month. The commission deduction will remain in effect
until revised or terminated. Changing the amount deducted or terminating the
deduction is done by submitting a written request to State Auto on a form that
will be provided by State Auto on request. Enrollment, or termination of
deductions will become effective as soon as practicable after a request is
received by State Auto. The request must be made using the State Auto form.

         The amounts deducted from commission checks pursuant to the Commission
Deduction Authorization will be commingled and forwarded monthly by State Auto
to the Bank with a list of the amounts deducted for each Participant's account.
State Auto has reserved the right to terminate the Plan and to discontinue use
of its commission deduction facilities for this purpose at any time.

DIVIDEND DISBURSEMENTS

         Dividends earned on shares in the Participant's account, as they become
payable by the Company, will be remitted by the Bank to each Participant by
check.

TERMINATION OF PARTICIPATION

         A Participant may terminate his or her account at any time by notifying
the Bank, in writing, at the following address: National City Bank, P.O. Box
92301, Cleveland, Ohio 44193-0900, providing a copy to State Auto.

         Any questions or correspondence about the Plan should be addressed to:
National City Bank at the same address shown above. The telephone number of
National City Bank is (216) 575-2658 or 1-800-622-8100 (extension 2658).